Bill Bryson《A Short History of Nearly Everything》16-22

part v   life itself

The more i examine the universe and study the details of its architecture,the more evidence i find that the universe in some sense must have known we were coming. -Freeman Dyson

16    LONELY PLANET

it isn’t easy being an organism. in the whole universe, as far as we yet know, there is only one place, an inconspicuous outpost of the milky way called earth, that will sustain you,and even it can be pretty grudging.

from the bottom of the deepest ocean trench to the top of the highest mountain, the zone that covers nearly the whole of known life, is only something over a dozen miles—not much when set against the roominess of the cosmos at large.

for humans it is even worse because we happen to belong to the portion of living things that took the rash but venturesome decision 400 million years ago to crawl out of the seas and become land based and oxygen breathing. in consequence, no less than 99.5 percent of the world’s habitable space by volume, according to one estimate, is fundamentally—in practical terms completely—off-limits to us.

it isn’t simply that we can’t breathe in water, but that we couldn’t bear the pressures.

because water is about 1,300 times heavier than air, pressures rise swiftly as you descend—by the equivalent of one atmosphere for every ten meters (thirty-three feet) of depth. on land,if you rose to the top of a five-hundred-foot eminence—cologne cathedral or the Washington monument, say—the change in pressure would be so slight as to be indiscernible. at the same depth underwater, however, your veins would collapse and your lungs would compress to the approximate dimensions of a coke can. amazingly, people do voluntarily dive to such depths,without breathing apparatus, for the fun of it in a sport known as free diving. apparently the experience of having your internal organs rudely deformed is thought exhilarating (though not presumably as exhilarating as having them return to their former dimensions upon resurfacing). to reach such depths, however, divers must be dragged down, and quite briskly,by weights. without assistance, the deepest anyone has gone and lived to talk about it afterward was an Italian named umberto pelizzari, who in 1992 dove to a depth of 236 feet,lingered for a nanosecond, and then shot back to the surface. in terrestrial terms, 236 feet is just slightly over the length of one New York city block. so even in our most exuberant stunts we can hardly claim to be masters of the abyss.

other organisms do of course manage to deal with the pressures at depth, though quite how some of them do so is a mystery. the deepest point in the ocean is the mariana trench in the pacific. there, some seven miles down, the pressures rise to over sixteen thousand pounds persquare inch. we have managed once, briefly, to send humans to that depth in a sturdy diving vessel, yet it is home to colonies of amphipods, a type of crustacean similar to shrimp but transparent, which survive without any protection at all. most oceans are of course much shallower, but even at the average ocean depth of two and a half miles the pressure is equivalent to being squashed beneath a stack of fourteen loaded cement trucks.

nearly everyone, including the authors of some popular books on oceanography, assumes that the human body would crumple under the immense pressures of the deep ocean. in fact,this appears not to be the case. because we are made largely of water ourselves, and water is“virtually incompressible,” in the words of frances ashcroft of oxford university, “the bodyremains at the same pressure as the surrounding water, and is not crushed at depth.” it is the gases inside your body, particularly in the lungs, that cause the trouble. these do compress,though at what point the compression becomes fatal is not known. until quite recently it was thought that anyone diving to one hundred meters or so would die painfully as his or her lungs imploded or chest wall collapsed, but the free divers have repeatedly proved otherwise. itappears, according to ashcroft, that “humans may be more like whales and dolphins than had been expected.”

plenty else can go wrong, however. in the days of diving suits—the sort that wereconnected to the surface by long hoses—divers sometimes experienced a dreadedphenomenon known as “the squeeze.” this occurred when the surface pumps failed, leadingto a catastrophic loss of pressure in the suit. the air would leave the suit with such violencethat the hapless diver would be, all too literally, sucked up into the helmet and hosepipe.

when hauled to the surface, “all that is left in the suit are his bones and some rags of flesh,”

the biologist j. b. s. haldane wrote in 1947, adding for the benefit of doubters, “this hashappened.”

(incidentally, the original diving helmet, designed in 1823 by an englishman namedcharles deane, was intended not for diving but for fire-fighting. it was called a “smokehelmet,” but being made of metal it was hot and cumbersome and, as deane soon discovered,firefighters had no particular eagerness to enter burning structures in any form of attire, butmost especially not in something that heated up like a kettle and made them clumsy into thebargain. in an attempt to save his investment, deane tried it underwater and found it was idealfor salvage work.)the real terror of the deep, however, is the bends—not so much because they areunpleasant, though of course they are, as because they are so much more likely. the air webreathe is 80 percent nitrogen. put the human body under pressure, and that nitrogen istransformed into tiny bubbles that migrate into the blood and tissues. if the pressure ischanged too rapidly—as with a too-quick ascent by a diver—the bubbles trapped within thebody will begin to fizz in exactly the manner of a freshly opened bottle of champagne,clogging tiny blood vessels, depriving cells of oxygen, and causing pain so excruciating thatsufferers are prone to bend double in agony—hence “the bends.”

the bends have been an occupational hazard for sponge and pearl divers since timeimmemorial but didn’t attract much attention in the western world until the nineteenthcentury, and then it was among people who didn’t get wet at all (or at least not very wet andnot generally much above the ankles). they were caisson workers. caissons were encloseddry chambers built on riverbeds to facilitate the construction of bridge piers. they were filledwith compressed air, and often when the workers emerged after an extended period ofworking under this artificial pressure they experienced mild symptoms like tingling or itchyskin. but an unpredictable few felt more insistent pain in the joints and occasionally collapsedin agony, sometimes never to get up again.

it was all most puzzling. sometimes workers would go to bed feeling fine, but wake upparalyzed. sometimes they wouldn’t wake up at all. ashcroft relates a story concerning thedirectors of a new tunnel under the thames who held a celebratory banquet as the tunnelneared completion. to their consternation their champagne failed to fizz when uncorked inthe compressed air of the tunnel. however, when at length they emerged into the fresh air of alondon evening, the bubbles sprang instantly to fizziness, memorably enlivening thedigestive process.

apart from avoiding high-pressure environments altogether, only two strategies are reliablysuccessful against the bends. the first is to suffer only a very short exposure to the changes inpressure. that is why the free divers i mentioned earlier can descend to depths of five hundredfeet without ill effect. they don’t stay under long enough for the nitrogen in their system todissolve into their tissues. the other solution is to ascend by careful stages. this allows thelittle bubbles of nitrogen to dissipate harmlessly.

a great deal of what we know about surviving at extremes is owed to the extraordinaryfather-and-son team of john scott and j. b. s. haldane. even by the demanding standards ofbritish intellectuals, the haldanes were outstandingly eccentric. the senior haldane was bornin 1860 to an aristocratic scottish family (his brother was viscount haldane) but spent mostof his career in comparative modesty as a professor of physiology at oxford. he wasfamously absent-minded. once after his wife had sent him upstairs to change for a dinnerparty he failed to return and was discovered asleep in bed in his pajamas. when roused,haldane explained that he had found himself disrobing and assumed it was bedtime. his ideaof a vacation was to travel to cornwall to study hookworm in miners. aldous huxley, thenovelist grandson of t. h. huxley, who lived with the haldanes for a time, parodied him, atouch mercilessly, as the scientist edward tantamount in the novel point counter point .

haldane’s gift to diving was to work out the rest intervals necessary to manage an ascentfrom the depths without getting the bends, but his interests ranged across the whole ofphysiology, from studying altitude sickness in climbers to the problems of heatstroke in desertregions. he had a particular interest in the effects of toxic gases on the human body. tounderstand more exactly how carbon monoxide leaks killed miners, he methodically poisonedhimself, carefully taking and measuring his own blood samples the while. he quit only whenhe was on the verge of losing all muscle control and his blood saturation level had reached 56percent—a level, as trevor norton notes in his entertaining history of diving, stars beneaththe sea, only fractionally removed from nearly certain lethality.

haldane’s son jack, known to posterity as j.b.s., was a remarkable prodigy who took aninterest in his father’s work almost from infancy. at the age of three he was overhearddemanding peevishly of his father, “but is it oxyhaemoglobin or carboxyhaemoglobin?”

throughout his youth, the young haldane helped his father with experiments. by the time hewas a teenager, the two often tested gases and gas masks together, taking turns to see howlong it took them to pass out.

though j. b. s. haldane never took a degree in science (he studied classics at oxford), hebecame a brilliant scientist in his own right, mostly in cambridge. the biologist petermedawar, who spent his life around mental olympians, called him “the cleverest man i everknew.” huxley likewise parodied the younger haldane in his novel antic hay, but also usedhis ideas on genetic manipulation of humans as the basis for the plot of brave new world.

among many other achievements, haldane played a central role in marrying darwinian
principles of evolution to the genetic work of gregor mendel to produce what is known togeneticists as the modern synthesis.

perhaps uniquely among human beings, the younger haldane found world war i “a veryenjoyable experience” and freely admitted that he “enjoyed the opportunity of killing people.”

he was himself wounded twice. after the war he became a successful popularizer of scienceand wrote twenty-three books (as well as over four hundred scientific papers). his books arestill thoroughly readable and instructive, though not always easy to find. he also became anenthusiastic marxist. it has been suggested, not altogether cynically, that this was out of apurely contrarian instinct, and that if he had been born in the soviet union he would havebeen a passionate monarchist. at all events, most of his articles first appeared in thecommunist daily worker.

whereas his father’s principal interests concerned miners and poisoning, the youngerhaldane became obsessed with saving submariners and divers from the unpleasantconsequences of their work. with admiralty funding he acquired a decompression chamberthat he called the “pressure pot.” this was a metal cylinder into which three people at a timecould be sealed and subjected to tests of various types, all painful and nearly all dangerous.

volunteers might be required to sit in ice water while breathing “aberrant atmosphere” orsubjected to rapid changes of pressurization. in one experiment, haldane simulated adangerously hasty ascent to see what would happen. what happened was that the dentalfillings in his teeth exploded. “almost every experiment,” norton writes, “ended withsomeone having a seizure, bleeding, or vomiting.” the chamber was virtually soundproof, sothe only way for occupants to signal unhappiness or distress was to tap insistently on thechamber wall or to hold up notes to a small window.

on another occasion, while poisoning himself with elevated levels of oxygen, haldane hada fit so severe that he crushed several vertebrae. collapsed lungs were a routine hazard.

perforated eardrums were quite common, but, as haldane reassuringly noted in one of hisessays, “the drum generally heals up; and if a hole remains in it, although one is somewhatdeaf, one can blow tobacco smoke out of the ear in question, which is a socialaccomplishment.”

what was extraordinary about this was not that haldane was willing to subject himself tosuch risk and discomfort in the pursuit of science, but that he had no trouble talkingcolleagues and loved ones into climbing into the chamber, too. sent on a simulated descent,his wife once had a fit that lasted thirteen minutes. when at last she stopped bouncing acrossthe floor, she was helped to her feet and sent home to cook dinner. haldane happily employedwhoever happened to be around, including on one memorable occasion a former primeminister of spain, juan negrín. dr. negrín complained afterward of minor tingling and “acurious velvety sensation on the lips” but otherwise seems to have escaped unharmed. he mayhave considered himself very lucky. a similar experiment with oxygen deprivation lefthaldane without feeling in his buttocks and lower spine for six years.

among haldane’s many specific preoccupations was nitrogen intoxication. for reasons thatare still poorly understood, beneath depths of about a hundred feet nitrogen becomes apowerful intoxicant. under its influence divers had been known to offer their air hoses topassing fish or decide to try to have a smoke break. it also produced wild mood swings. inone test, haldane noted, the subject “alternated between depression and elation, at onemoment begging to be decompressed because he felt ‘bloody awful’ and the next minutelaughing and attempting to interfere with his colleague’s dexterity test.” in order to measure
the rate of deterioration in the subject, a scientist had to go into the chamber with thevolunteer to conduct simple mathematical tests. but after a few minutes, as haldane laterrecalled, “the tester was usually as intoxicated as the testee, and often forgot to press thespindle of his stopwatch, or to take proper notes.” the cause of the inebriation is even now amystery. it is thought that it may be the same thing that causes alcohol intoxication, but as noone knows for certain what causes that we are none the wiser. at all events, without thegreatest care, it is easy to get in trouble once you leave the surface world.

which brings us back (well, nearly) to our earlier observation that earth is not the easiestplace to be an organism, even if it is the only place. of the small portion of the planet’ssurface that is dry enough to stand on, a surprisingly large amount is too hot or cold or dry orsteep or lofty to be of much use to us. partly, it must be conceded, this is our fault. in terms ofadaptability, humans are pretty amazingly useless. like most animals, we don’t much likereally hot places, but because we sweat so freely and easily stroke, we are especiallyvulnerable. in the worst circumstances—on foot without water in a hot desert—most peoplewill grow delirious and keel over, possibly never to rise again, in no more than six or sevenhours. we are no less helpless in the face of cold. like all mammals, humans are good atgenerating heat but—because we are so nearly hairless—not good at keeping it. even in quitemild weather half the calories you burn go to keep your body warm. of course, we cancounter these frailties to a large extent by employing clothing and shelter, but even so theportions of earth on which we are prepared or able to live are modest indeed: just 12 percentof the total land area, and only 4 percent of the whole surface if you include the seas.

yet when you consider conditions elsewhere in the known universe, the wonder is not thatwe use so little of our planet but that we have managed to find a planet that we can use even abit of. you have only to look at our own solar system—or, come to that, earth at certainperiods in its own history—to appreciate that most places are much harsher and much lessamenable to life than our mild, blue watery globe.

so far space scientists have discovered about seventy planets outside the solar system, outof the ten billion trillion or so that are thought to be out there, so humans can hardly claim tospeak with authority on the matter, but it appears that if you wish to have a planet suitable forlife, you have to be just awfully lucky, and the more advanced the life, the luckier you have tobe. various observers have identified about two dozen particularly helpful breaks we havehad on earth, but this is a flying survey so we’ll distill them down to the principal four. theyare:

excellent location.we are, to an almost uncanny degree, the right distance from the right sortof star, one that is big enough to radiate lots of energy, but not so big as to burn itself outswiftly. it is a curiosity of physics that the larger a star the more rapidly it burns. had our sunbeen ten times as massive, it would have exhausted itself after ten million years instead of tenbillion and we wouldn’t be here now. we are also fortunate to orbit where we do. too muchnearer and everything on earth would have boiled away. much farther away and everythingwould have frozen.

in 1978, an astrophysicist named michael hart made some calculations and concluded thatearth would have been uninhabitable had it been just 1 percent farther from or 5 percent
closer to the sun. that’s not much, and in fact it wasn’t enough. the figures have since beenrefined and made a little more generous—5 percent nearer and 15 percent farther are thoughtto be more accurate assessments for our zone of habitability—but that is still a narrow belt.

1to appreciate just how narrow, you have only to look at venus. venus is only twenty-fivemillion miles closer to the sun than we are. the sun’s warmth reaches it just two minutesbefore it touches us. in size and composition, venus is very like earth, but the smalldifference in orbital distance made all the difference to how it turned out. it appears thatduring the early years of the solar system venus was only slightly warmer than earth andprobably had oceans. but those few degrees of extra warmth meant that venus could not holdon to its surface water, with disastrous consequences for its climate. as its water evaporated,the hydrogen atoms escaped into space, and the oxygen atoms combined with carbon to forma dense atmosphere of the greenhouse gas co2. venus became stifling. although people ofmy age will recall a time when astronomers hoped that venus might harbor life beneath itspadded clouds, possibly even a kind of tropical verdure, we now know that it is much toofierce an environment for any kind of life that we can reasonably conceive of. its surfacetemperature is a roasting 470 degrees centigrade (roughly 900 degrees fahrenheit), which ishot enough to melt lead, and the atmospheric pressure at the surface is ninety times that ofearth, or more than any human body could withstand. we lack the technology to make suitsor even spaceships that would allow us to visit. our knowledge of venus’s surface is based ondistant radar imagery and some startled squawks from an unmanned soviet probe that wasdropped hopefully into the clouds in 1972 and functioned for barely an hour beforepermanently shutting down.

so that’s what happens when you move two light minutes closer to the sun. travel fartherout and the problem becomes not heat but cold, as mars frigidly attests. it, too, was once amuch more congenial place, but couldn’t retain a usable atmosphere and turned into a frozenwaste.

but just being the right distance from the sun cannot be the whole story, for otherwise themoon would be forested and fair, which patently it is not. for that you need to have:

the right kind of planet.i don’t imagine even many geophysicists, when asked to counttheir blessings, would include living on a planet with a molten interior, but it’s a pretty nearcertainty that without all that magma swirling around beneath us we wouldn’t be here now.

apart from much else, our lively interior created the outgassing that helped to build anatmosphere and provided us with the magnetic field that shields us from cosmic radiation. italso gave us plate tectonics, which continually renews and rumples the surface. if earth wereperfectly smooth, it would be covered everywhere with water to a depth of four kilometers.

there might be life in that lonesome ocean, but there certainly wouldn’t be baseball.

in addition to having a beneficial interior, we also have the right elements in the correctproportions. in the most literal way, we are made of the right stuff. this is so crucial to ourwell-being that we are going to discuss it more fully in a minute, but first we need to considerthe two remaining factors, beginning with another one that is often overlooked:

1the discovery of extremophiles in the boiling mudpots of yellowstone and similar organisms found elsewheremade scientists realize that actually life of a type could range much farther than that-even, perhaps, beneath theicy skin of pluto. what we are talking about here are the conditions that would produce reasonably complexsurface creatures.

we’re a twin planet.not many of us normally think of the moon as a companion planet,but that is in effect what it is. most moons are tiny in relation to their master planet. themartian satellites of phobos and deimos, for instance, are only about ten kilometers indiameter. our moon, however, is more than a quarter the diameter of the earth, which makesours the only planet in the solar system with a sizeable moon in comparison to itself (exceptpluto, which doesn’t really count because pluto is itself so small), and what a difference thatmakes to us.

without the moon’s steadying influence, the earth would wobble like a dying top, withgoodness knows what consequences for climate and weather. the moon’s steady gravitationalinfluence keeps the earth spinning at the right speed and angle to provide the sort of stabilitynecessary for the long and successful development of life. this won’t go on forever. themoon is slipping from our grasp at a rate of about 1.5 inches a year. in another two billionyears it will have receded so far that it won’t keep us steady and we will have to come up withsome other solution, but in the meantime you should think of it as much more than just apleasant feature in the night sky.

for a long time, astronomers assumed that the moon and earth either formed together orthat the earth captured the moon as it drifted by. we now believe, as you will recall from anearlier chapter, that about 4.5 billion years ago a mars-sized object slammed into earth,blowing out enough material to create the moon from the debris. this was obviously a verygood thing for us—but especially so as it happened such a long time ago. if it had happened in1896 or last wednesday clearly we wouldn’t be nearly so pleased about it. which brings us toour fourth and in many ways most crucial consideration:

timing.the universe is an amazingly fickle and eventful place, and our existence within itis a wonder. if a long and unimaginably complex sequence of events stretching back 4.6billion years or so hadn’t played out in a particular manner at particular times—if, to take justone obvious instance, the dinosaurs hadn’t been wiped out by a meteor when they were—youmight well be six inches long, with whiskers and a tail, and reading this in a burrow.

we don’t really know for sure because we have nothing else to compare our own existenceto, but it seems evident that if you wish to end up as a moderately advanced, thinking society,you need to be at the right end of a very long chain of outcomes involving reasonable periodsof stability interspersed with just the right amount of stress and challenge (ice ages appear tobe especially helpful in this regard) and marked by a total absence of real cataclysm. as weshall see in the pages that remain to us, we are very lucky to find ourselves in that position.

and on that note, let us now turn briefly to the elements that made us.

there are ninety-two naturally occurring elements on earth, plus a further twenty or so thathave been created in labs, but some of these we can immediately put to one side—as, in fact,chemists themselves tend to do. not a few of our earthly chemicals are surprisingly littleknown. astatine, for instance, is practically unstudied. it has a name and a place on theperiodic table (next door to marie curie’s polonium), but almost nothing else. the problem
isn’t scientific indifference, but rarity. there just isn’t much astatine out there. the mostelusive element of all, however, appears to be francium, which is so rare that it is thought thatour entire planet may contain, at any given moment, fewer than twenty francium atoms.

altogether only about thirty of the naturally occurring elements are widespread on earth, andbarely half a dozen are of central importance to life.

as you might expect, oxygen is our most abundant element, accounting for just under 50percent of the earth’s crust, but after that the relative abundances are often surprising. whowould guess, for instance, that silicon is the second most common element on earth or thattitanium is tenth? abundance has little to do with their familiarity or utility to us. many of themore obscure elements are actually more common than the better-known ones. there is morecerium on earth than copper, more neodymium and lanthanum than cobalt or nitrogen. tinbarely makes it into the top fifty, eclipsed by such relative obscurities as praseodymium,samarium, gadolinium, and dysprosium.

abundance also has little to do with ease of detection. aluminum is the fourth mostcommon element on earth, accounting for nearly a tenth of everything that’s underneath yourfeet, but its existence wasn’t even suspected until it was discovered in the nineteenth centuryby humphry davy, and for a long time after that it was treated as rare and precious. congressnearly put a shiny lining of aluminum foil atop the washington monument to show what aclassy and prosperous nation we had become, and the french imperial family in the sameperiod discarded the state silver dinner service and replaced it with an aluminum one. thefashion was cutting edge even if the knives weren’t.

nor does abundance necessarily relate to importance. carbon is only the fifteenth mostcommon element, accounting for a very modest 0.048 percent of earth’s crust, but we wouldbe lost without it. what sets the carbon atom apart is that it is shamelessly promiscuous. it isthe party animal of the atomic world, latching on to many other atoms (including itself) andholding tight, forming molecular conga lines of hearty robustness—the very trick of naturenecessary to build proteins and dna. as paul davies has written: “if it wasn’t for carbon, lifeas we know it would be impossible. probably any sort of life would be impossible.” yetcarbon is not all that plentiful even in humans, who so vitally depend on it. of every 200atoms in your body, 126 are hydrogen, 51 are oxygen, and just 19 are carbon.

2other elements are critical not for creating life but for sustaining it. we need iron tomanufacture hemoglobin, and without it we would die. cobalt is necessary for the creation ofvitamin b12. potassium and a very little sodium are literally good for your nerves.

molybdenum, manganese, and vanadium help to keep your enzymes purring. zinc—bless it—oxidizes alcohol.

we have evolved to utilize or tolerate these things—we could hardly be here otherwise—but even then we live within narrow ranges of acceptance. selenium is vital to all of us, buttake in just a little too much and it will be the last thing you ever do. the degree to whichorganisms require or tolerate certain elements is a relic of their evolution. sheep and cattlenow graze side by side, but actually have very different mineral requirements. modern cattleneed quite a lot of copper because they evolved in parts of europe and africa where copperwas abundant. sheep, on the other hand, evolved in copper-poor areas of asia minor. as arule, and not surprisingly, our tolerance for elements is directly proportionate to their2of the remaining four, three are nitrogen and the remaining atom is divided among all the other elements.

abundance in the earth’s crust. we have evolved to expect, and in some cases actually need,the tiny amounts of rare elements that accumulate in the flesh or fiber that we eat. but step upthe doses, in some cases by only a tiny amount, and we can soon cross a threshold. much ofthis is only imperfectly understood. no one knows, for example, whether a tiny amount ofarsenic is necessary for our well-being or not. some authorities say it is; some not. all that iscertain is that too much of it will kill you.

the properties of the elements can become more curious still when they are combined.

oxygen and hydrogen, for instance, are two of the most combustion-friendly elements around,but put them together and they make incombustible water.

3odder still in combination aresodium, one of the most unstable of all elements, and chlorine, one of the most toxic. drop asmall lump of pure sodium into ordinary water and it will explode with enough force to kill.

chlorine is even more notoriously hazardous. though useful in small concentrations forkilling microorganisms (it’s chlorine you smell in bleach), in larger volumes it is lethal.

chlorine was the element of choice for many of the poison gases of the first world war. and,as many a sore-eyed swimmer will attest, even in exceedingly dilute form the human bodydoesn’t appreciate it. yet put these two nasty elements together and what do you get? sodiumchloride—common table salt.

by and large, if an element doesn’t naturally find its way into our systems—if it isn’tsoluble in water, say—we tend to be intolerant of it. lead poisons us because we were neverexposed to it until we began to fashion it into food vessels and pipes for plumbing. (notincidentally, lead’s symbol is pb, for the latin plumbum, the source word for our modernplumbing.) the romans also flavored their wine with lead, which may be part of the reasonthey are not the force they used to be. as we have seen elsewhere, our own performance withlead (not to mention mercury, cadmium, and all the other industrial pollutants with which weroutinely dose ourselves) does not leave us a great deal of room for smirking. when elementsdon’t occur naturally on earth, we have evolved no tolerance for them, and so they tend to beextremely toxic to us, as with plutonium. our tolerance for plutonium is zero: there is no levelat which it is not going to make you want to lie down.

i have brought you a long way to make a small point: a big part of the reason that earthseems so miraculously accommodating is that we evolved to suit its conditions. what wemarvel at is not that it is suitable to life but that it is suitable to our life—and hardlysurprising, really. it may be that many of the things that make it so splendid to us—well-proportioned sun, doting moon, sociable carbon, more magma than you can shake a stick at,and all the rest—seem splendid simply because they are what we were born to count on. noone can altogether say.

other worlds may harbor beings thankful for their silvery lakes of mercury and driftingclouds of ammonia. they may be delighted that their planet doesn’t shake them silly with itsgrinding plates or spew messy gobs of lava over the landscape, but rather exists in apermanent nontectonic tranquility. any visitors to earth from afar would almost certainly, atthe very least, be bemused to find us living in an atmosphere composed of nitrogen, a gassulkily disinclined to react with anything, and oxygen, which is so partial to combustion thatwe must place fire stations throughout our cities to protect ourselves from its livelier effects.

but even if our visitors were oxygen-breathing bipeds with shopping malls and a fondness for3oxygen itself is not combustible; it merely facilitates the combus tion of other things. this is just as well, for ifoxygen were corn bustible, each time you lit a match all the air around you would bur into flame. hydrogen gas,on the other hand, is extremely corn bustible, as the dirigible hindenburg demonstrated on may 6, 193 inlakehurst, new jersey, when its hydrogen fuel burst explosive) into flame, killing thirty-six people.

action movies, it is unlikely that they would find earth ideal. we couldn’t even give themlunch because all our foods contain traces of manganese, selenium, zinc, and other elementalparticles at least some of which would be poisonous to them. to them earth might not seem awondrously congenial place at all.

the physicist richard feynman used to make a joke about a posteriori conclusions, as theyare called. “you know, the most amazing thing happened to me tonight,” he would say. “isaw a car with the license plate arw 357. can you imagine? of all the millions of licenseplates in the state, what was the chance that i would see that particular one tonight?

amazing!” his point, of course, was that it is easy to make any banal situation seemextraordinary if you treat it as fateful.

so it is possible that the events and conditions that led to the rise of life on earth are notquite as extraordinary as we like to think. still, they were extraordinary enough, and one thingis certain: they will have to do until we find some better.

17   INTO THE TROPOSPHERE

thank goodness for the atmosphere. it keeps us warm. without it, earth would be alifeless ball of ice with an average temperature of minus 60 degrees fahrenheit. in addition,the atmosphere absorbs or deflects incoming swarms of cosmic rays, charged particles,ultraviolet rays, and the like. altogether, the gaseous padding of the atmosphere is equivalentto a fifteen-foot thickness of protective concrete, and without it these invisible visitors fromspace would slice through us like tiny daggers. even raindrops would pound us senseless if itweren’t for the atmosphere’s slowing drag.

the most striking thing about our atmosphere is that there isn’t very much of it. it extendsupward for about 120 miles, which might seem reasonably bounteous when viewed fromground level, but if you shrank the earth to the size of a standard desktop globe it would onlybe about the thickness of a couple of coats of varnish.

for scientific convenience, the atmosphere is divided into four unequal layers: troposphere,stratosphere, mesosphere, and ionosphere (now often called the thermosphere). thetroposphere is the part that’s dear to us. it alone contains enough warmth and oxygen to allowus to function, though even it swiftly becomes uncongenial to life as you climb up through it.

from ground level to its highest point, the troposphere (or “turning sphere”) is about ten milesthick at the equator and no more than six or seven miles high in the temperate latitudes wheremost of us live. eighty percent of the atmosphere’s mass, virtually all the water, and thusvirtually all the weather are contained within this thin and wispy layer. there really isn’tmuch between you and oblivion.

beyond the troposphere is the stratosphere. when you see the top of a storm cloudflattening out into the classic anvil shape, you are looking at the boundary between thetroposphere and stratosphere. this invisible ceiling is known as the tropopause and wasdiscovered in 1902 by a frenchman in a balloon, léon-philippe teisserenc de bort. pause inthis sense doesn’t mean to stop momentarily but to cease altogether; it’s from the same greekroot as menopause. even at its greatest extent, the tropopause is not very distant. a fastelevator of the sort used in modern skyscrapers could get you there in about twenty minutes,though you would be well advised not to make the trip. such a rapid ascent withoutpressurization would, at the very least, result in severe cerebral and pulmonary edemas, adangerous excess of fluids in the body’s tissues. when the doors opened at the viewingplatform, anyone inside would almost certainly be dead or dying. even a more measuredascent would be accompanied by a great deal of discomfort. the temperature six miles up canbe -70 degrees fahrenheit, and you would need, or at least very much appreciate,supplementary oxygen.

after you have left the troposphere the temperature soon warms up again, to about 40degrees fahrenheit, thanks to the absorptive effects of ozone (something else de bortdiscovered on his daring 1902 ascent). it then plunges to as low as -130 degrees fahrenheit inthe mesosphere before skyrocketing to 2,700 degrees fahrenheit or more in the aptly namedbut very erratic thermosphere, where temperatures can vary by a thousand degrees from day
to night—though it must be said that “temperature” at such a height becomes a somewhatnotional concept. temperature is really just a measure of the activity of molecules. at sealevel, air molecules are so thick that one molecule can move only the tiniest distance—aboutthree-millionths of an inch, to be precise—before banging into another. because trillions ofmolecules are constantly colliding, a lot of heat gets exchanged. but at the height of thethermosphere, at fifty miles or more, the air is so thin that any two molecules will be milesapart and hardly ever come in contact. so although each molecule is very warm, there are fewinteractions between them and thus little heat transference. this is good news for satellitesand spaceships because if the exchange of heat were more efficient any man-made objectorbiting at that level would burst into flame.

even so, spaceships have to take care in the outer atmosphere, particularly on return trips toearth, as the space shuttle columbia demonstrated all too tragically in february 2003.

although the atmosphere is very thin, if a craft comes in at too steep an angle—more thanabout 6 degrees—or too swiftly it can strike enough molecules to generate drag of anexceedingly combustible nature. conversely, if an incoming vehicle hit the thermosphere attoo shallow an angle, it could well bounce back into space, like a pebble skipped across water.

but you needn’t venture to the edge of the atmosphere to be reminded of what hopelesslyground-hugging beings we are. as anyone who has spent time in a lofty city will know, youdon’t have to rise too many thousands of feet from sea level before your body begins toprotest. even experienced mountaineers, with the benefits of fitness, training, and bottledoxygen, quickly become vulnerable at height to confusion, nausea, exhaustion, frostbite,hypothermia, migraine, loss of appetite, and a great many other stumbling dysfunctions. in ahundred emphatic ways the human body reminds its owner that it wasn’t designed to operateso far above sea level.

“even under the most favorable circumstances,” the climber peter habeler has written ofconditions atop everest, “every step at that altitude demands a colossal effort of will. youmust force yourself to make every movement, reach for every handhold. you are perpetuallythreatened by a leaden, deadly fatigue.” in the other side of everest, the british mountaineerand filmmaker matt dickinson records how howard somervell, on a 1924 british expeditionup everest, “found himself choking to death after a piece of infected flesh came loose andblocked his windpipe.” with a supreme effort somervell managed to cough up theobstruction. it turned out to be “the entire mucus lining of his larynx.”

bodily distress is notorious above 25,000 feet—the area known to climbers as the deathzone—but many people become severely debilitated, even dangerously ill, at heights of nomore than 15,000 feet or so. susceptibility has little to do with fitness. grannies sometimescaper about in lofty situations while their fitter offspring are reduced to helpless, groaningheaps until conveyed to lower altitudes.

the absolute limit of human tolerance for continuous living appears to be about 5,500meters, or 18,000 feet, but even people conditioned to living at altitude could not tolerate suchheights for long. frances ashcroft, in life at the extremes, notes that there are andean sulfurmines at 5,800 meters, but that the miners prefer to descend 460 meters each evening andclimb back up the following day, rather than live continuously at that elevation. people whohabitually live at altitude have often spent thousands of years developing disproportionatelylarge chests and lungs, increasing their density of oxygen-bearing red blood cells by almost athird, though there are limits to how much thickening with red cells the blood supply can
stand. moreover, above 5,500 meters even the most well-adapted women cannot provide agrowing fetus with enough oxygen to bring it to its full term.

in the 1780s when people began to make experimental balloon ascents in europe,something that surprised them was how chilly it got as they rose. the temperature drops about3 degrees fahrenheit with every thousand feet you climb. logic would seem to indicate thatthe closer you get to a source of heat, the warmer you would feel. part of the explanation isthat you are not really getting nearer the sun in any meaningful sense. the sun is ninety-threemillion miles away. to move a couple of thousand feet closer to it is like taking one stepcloser to a bushfire in australia when you are standing in ohio, and expecting to smell smoke.

the answer again takes us back to the question of the density of molecules in the atmosphere.

sunlight energizes atoms. it increases the rate at which they jiggle and jounce, and in theirenlivened state they crash into one another, releasing heat. when you feel the sun warm onyour back on a summer’s day, it’s really excited atoms you feel. the higher you climb, thefewer molecules there are, and so the fewer collisions between them.

air is deceptive stuff. even at sea level, we tend to think of the air as being ethereal and allbut weightless. in fact, it has plenty of bulk, and that bulk often exerts itself. as a marinescientist named wyville thomson wrote more than a century ago: “we sometimes find whenwe get up in the morning, by a rise of an inch in the barometer, that nearly half a ton has beenquietly piled upon us during the night, but we experience no inconvenience, rather a feeling ofexhilaration and buoyancy, since it requires a little less exertion to move our bodies in thedenser medium.” the reason you don’t feel crushed under that extra half ton of pressure is thesame reason your body would not be crushed deep beneath the sea: it is made mostly ofincompressible fluids, which push back, equalizing the pressures within and without.

but get air in motion, as with a hurricane or even a stiff breeze, and you will quickly bereminded that it has very considerable mass. altogether there are about 5,200 million milliontons of air around us—25 million tons for every square mile of the planet—a notinconsequential volume. when you get millions of tons of atmosphere rushing past at thirty orforty miles an hour, it’s hardly a surprise that limbs snap and roof tiles go flying. as anthonysmith notes, a typical weather front may consist of 750 million tons of cold air pinnedbeneath a billion tons of warmer air. hardly a wonder that the result is at timesmeteorologically exciting.

certainly there is no shortage of energy in the world above our heads. one thunderstorm, ithas been calculated, can contain an amount of energy equivalent to four days’ use ofelectricity for the whole united states. in the right conditions, storm clouds can rise to heightsof six to ten miles and contain updrafts and downdrafts of one hundred miles an hour. theseare often side by side, which is why pilots don’t want to fly through them. in all, the internalturmoil particles within the cloud pick up electrical charges. for reasons not entirelyunderstood the lighter particles tend to become positively charged and to be wafted by aircurrents to the top of the cloud. the heavier particles linger at the base, accumulating negativecharges. these negatively charged particles have a powerful urge to rush to the positivelycharged earth, and good luck to anything that gets in their way. a bolt of lightning travels at270,000 miles an hour and can heat the air around it to a decidedly crisp 50,000 degreesfahrenheit, several times hotter than the surface of the sun. at any one moment 1,800thunderstorms are in progress around the globe—some 40,000 a day. day and night across theplanet every second about a hundred lightning bolts hit the ground. the sky is a lively place.

much of our knowledge of what goes on up there is surprisingly recent. jet streams, usuallylocated about 30,000 to 35,000 feet up, can bowl along at up to 180 miles an hour and vastlyinfluence weather systems over whole continents, yet their existence wasn’t suspected untilpilots began to fly into them during the second world war. even now a great deal ofatmospheric phenomena is barely understood. a form of wave motion popularly known asclear-air turbulence occasionally enlivens airplane flights. about twenty such incidents a yearare serious enough to need reporting. they are not associated with cloud structures oranything else that can be detected visually or by radar. they are just pockets of startlingturbulence in the middle of tranquil skies. in a typical incident, a plane en route fromsingapore to sydney was flying over central australia in calm conditions when it suddenlyfell three hundred feet—enough to fling unsecured people against the ceiling. twelve peoplewere injured, one seriously. no one knows what causes such disruptive cells of air.

the process that moves air around in the atmosphere is the same process that drives theinternal engine of the planet, namely convection. moist, warm air from the equatorial regionsrises until it hits the barrier of the tropopause and spreads out. as it travels away from theequator and cools, it sinks. when it hits bottom, some of the sinking air looks for an area oflow pressure to fill and heads back for the equator, completing the circuit.

at the equator the convection process is generally stable and the weather predictably fair,but in temperate zones the patterns are far more seasonal, localized, and random, whichresults in an endless battle between systems of high-pressure air and low. low-pressuresystems are created by rising air, which conveys water molecules into the sky, forming cloudsand eventually rain. warm air can hold more moisture than cool air, which is why tropical andsummer storms tend to be the heaviest. thus low areas tend to be associated with clouds andrain, and highs generally spell sunshine and fair weather. when two such systems meet, itoften becomes manifest in the clouds. for instance, stratus clouds—those unlovable,featureless sprawls that give us our overcast skies—happen when moisture-bearing updraftslack the oomph to break through a level of more stable air above, and instead spread out, likesmoke hitting a ceiling. indeed, if you watch a smoker sometime, you can get a very goodidea of how things work by watching how smoke rises from a cigarette in a still room. atfirst, it goes straight up (this is called a laminar flow, if you need to impress anyone), and thenit spreads out in a diffused, wavy layer. the greatest supercomputer in the world, takingmeasurements in the most carefully controlled environment, cannot tell you what forms theseripplings will take, so you can imagine the difficulties that confront meteorologists when theytry to predict such motions in a spinning, windy, large-scale world.

what we do know is that because heat from the sun is unevenly distributed, differences inair pressure arise on the planet. air can’t abide this, so it rushes around trying to equalizethings everywhere. wind is simply the air’s way of trying to keep things in balance. airalways flows from areas of high pressure to areas of low pressure (as you would expect; thinkof anything with air under pressure—a balloon or an air tank—and think how insistently thatpressured air wants to get someplace else), and the greater the discrepancy in pressures thefaster the wind blows.

incidentally, wind speeds, like most things that accumulate, grow exponentially, so a windblowing at two hundred miles an hour is not simply ten times stronger than a wind blowing attwenty miles an hour, but a hundred times stronger—and hence that much more destructive.

introduce several million tons of air to this accelerator effect and the result can be exceedingly
energetic. a tropical hurricane can release in twenty-four hours as much energy as a rich,medium-sized nation like britain or france uses in a year.

the impulse of the atmosphere to seek equilibrium was first suspected by edmondhalley—the man who was everywhere—and elaborated upon in the eighteenth century by hisfellow briton george hadley, who saw that rising and falling columns of air tended toproduce “cells” (known ever since as “hadley cells”). though a lawyer by profession, hadleyhad a keen interest in the weather (he was, after all, english) and also suggested a linkbetween his cells, the earth’s spin, and the apparent deflections of air that give us our tradewinds. however, it was an engineering professor at the école polytechnique in paris,gustave-gaspard de coriolis, who worked out the details of these interactions in 1835, andthus we call it the coriolis effect. (coriolis’s other distinction at the school was to introducewatercoolers, which are still known there as corios, apparently.) the earth revolves at a brisk1,041 miles an hour at the equator, though as you move toward the poles the rate slopes offconsiderably, to about 600 miles an hour in london or paris, for instance. the reason for thisis self-evident when you think about it. if you are on the equator the spinning earth has tocarry you quite a distance—about 40,000 kilometers—to get you back to the same spot. if youstand beside the north pole, however, you may need travel only a few feet to complete arevolution, yet in both cases it takes twenty-four hours to get you back to where you began.

therefore, it follows that the closer you get to the equator the faster you must be spinning.

the coriolis effect explains why anything moving through the air in a straight line laterallyto the earth’s spin will, given enough distance, seem to curve to the right in the northernhemisphere and to the left in the southern as the earth revolves beneath it. the standard wayto envision this is to imagine yourself at the center of a large carousel and tossing a ball tosomeone positioned on the edge. by the time the ball gets to the perimeter, the target personhas moved on and the ball passes behind him. from his perspective, it looks as if it has curvedaway from him. that is the coriolis effect, and it is what gives weather systems their curl andsends hurricanes spinning off like tops. the coriolis effect is also why naval guns firingartillery shells have to adjust to left or right; a shell fired fifteen miles would otherwisedeviate by about a hundred yards and plop harmlessly into the sea.

considering the practical and psychological importance of the weather to nearly everyone,it’s surprising that meteorology didn’t really get going as a science until shortly before theturn of the nineteenth century (though the term meteorology itself had been around since1626, when it was coined by a t. granger in a book of logic).

part of the problem was that successful meteorology requires the precise measurement oftemperatures, and thermometers for a long time proved more difficult to make than you mightexpect. an accurate reading was dependent on getting a very even bore in a glass tube, andthat wasn’t easy to do. the first person to crack the problem was daniel gabriel fahrenheit, adutch maker of instruments, who produced an accurate thermometer in 1717. however, forreasons unknown he calibrated the instrument in a way that put freezing at 32 degrees andboiling at 212 degrees. from the outset this numeric eccentricity bothered some people, and in1742 anders celsius, a swedish astronomer, came up with a competing scale. in proof of theproposition that inventors seldom get matters entirely right, celsius made boiling point zeroand freezing point 100 on his scale, but that was soon reversed.

the person most frequently identified as the father of modern meteorology was an englishpharmacist named luke howard, who came to prominence at the beginning of the nineteenthcentury. howard is chiefly remembered now for giving cloud types their names in 1803.

although he was an active and respected member of the linnaean society and employedlinnaean principles in his new scheme, howard chose the rather more obscure askesiansociety as the forum to announce his new system of classification. (the askesian society,you may just recall from an earlier chapter, was the body whose members were unusuallydevoted to the pleasures of nitrous oxide, so we can only hope they treated howard’spresentation with the sober attention it deserved. it is a point on which howard scholars arecuriously silent.)howard divided clouds into three groups: stratus for the layered clouds, cumulus for thefluffy ones (the word means “heaped” in latin), and cirrus (meaning “curled”) for the high,thin feathery formations that generally presage colder weather. to these he subsequentlyadded a fourth term, nimbus (from the latin for “cloud”), for a rain cloud. the beauty ofhoward’s system was that the basic components could be freely recombined to describe everyshape and size of passing cloud—stratocumulus, cirrostratus, cumulocongestus, and so on. itwas an immediate hit, and not just in england. the poet johann von goethe in germany wasso taken with the system that he dedicated four poems to howard.

howard’s system has been much added to over the years, so much so that the encyclopedicif little read international cloud atlas runs to two volumes, but interestingly virtually all thepost-howard cloud types—mammatus, pileus, nebulosis, spissatus, floccus, and mediocris area sampling—have never caught on with anyone outside meteorology and not terribly muchthere, i’m told. incidentally, the first, much thinner edition of that atlas, produced in 1896,divided clouds into ten basic types, of which the plumpest and most cushiony-looking wasnumber nine, cumulonimbus.

1that seems to have been the source of the expression “to be oncloud nine.”

for all the heft and fury of the occasional anvil-headed storm cloud, the average cloud isactually a benign and surprisingly insubstantial thing. a fluffy summer cumulus severalhundred yards to a side may contain no more than twenty-five or thirty gallons of water—“about enough to fill a bathtub,” as james trefil has noted. you can get some sense of theimmaterial quality of clouds by strolling through fog—which is, after all, nothing more than acloud that lacks the will to fly. to quote trefil again: “if you walk 100 yards through a typicalfog, you will come into contact with only about half a cubic inch of water—not enough togive you a decent drink.” in consequence, clouds are not great reservoirs of water. only about0.035 percent of the earth’s fresh water is floating around above us at any moment.

depending on where it falls, the prognosis for a water molecule varies widely. if it lands infertile soil it will be soaked up by plants or reevaporated directly within hours or days. if itfinds its way down to the groundwater, however, it may not see sunlight again for manyyears—thousands if it gets really deep. when you look at a lake, you are looking at acollection of molecules that have been there on average for about a decade. in the ocean theresidence time is thought to be more like a hundred years. altogether about 60 percent of1if you have ever been struck by how beautifully crisp and well defined the edges of cumulus clouds tend to be,while other clouds are more blurry, the explanation is that in a cumulus cloud there is a pronounced boundarybetween the moist interior of the cloud and the dry air beyond it. any water molecule that strays beyond the edgeof the cloud is immediately zapped by the dry air beyond, allowing the cloud to keep its fine edge. much highercirrus clouds are composed of ice, and the zone between the edge of the cloud and the air beyond is not soclearly delineated, which is why they tend to be blurry at the edges.

water molecules in a rainfall are returned to the atmosphere within a day or two. onceevaporated, they spend no more than a week or so—drury says twelve days—in the skybefore falling again as rain.

evaporation is a swift process, as you can easily gauge by the fate of a puddle on asummer’s day. even something as large as the mediterranean would dry out in a thousandyears if it were not continually replenished. such an event occurred a little under six millionyears ago and provoked what is known to science as the messinian salinity crisis. whathappened was that continental movement closed the strait of gibraltar. as the mediterraneandried, its evaporated contents fell as freshwater rain into other seas, mildly diluting theirsaltiness—indeed, making them just dilute enough to freeze over larger areas than normal.

the enlarged area of ice bounced back more of the sun’s heat and pushed earth into an iceage. so at least the theory goes.

what is certainly true, as far as we can tell, is that a little change in the earth’s dynamicscan have repercussions beyond our imagining. such an event, as we shall see a little furtheron, may even have created us.

oceans are the real powerhouse of the planet’s surface behavior. indeed, meteorologistsincreasingly treat oceans and atmosphere as a single system, which is why we must give thema little of our attention here. water is marvelous at holding and transporting heat. every day,the gulf stream carries an amount of heat to europe equivalent to the world’s output of coalfor ten years, which is why britain and ireland have such mild winters compared with canadaand russia.

but water also warms slowly, which is why lakes and swimming pools are cold even on thehottest days. for that reason there tends to be a lag in the official, astronomical start of aseason and the actual feeling that that season has started. so spring may officially start in thenorthern hemisphere in march, but it doesn’t feel like it in most places until april at the veryearliest.

the oceans are not one uniform mass of water. their differences in temperature, salinity,depth, density, and so on have huge effects on how they move heat around, which in turnaffects climate. the atlantic, for instance, is saltier than the pacific, and a good thing too. thesaltier water is the denser it is, and dense water sinks. without its extra burden of salt, theatlantic currents would proceed up to the arctic, warming the north pole but deprivingeurope of all that kindly warmth. the main agent of heat transfer on earth is what is knownas thermohaline circulation, which originates in slow, deep currents far below the surface—aprocess first detected by the scientist-adventurer count von rumford in 1797.

2what happensis that surface waters, as they get to the vicinity of europe, grow dense and sink to greatdepths and begin a slow trip back to the southern hemisphere. when they reach antarctica,they are caught up in the antarctic circumpolar current, where they are driven onward intothe pacific. the process is very slow—it can take 1,500 years for water to travel from the2the term means a number of things to different people, it appears. in november 2002, carl wunsch of mitpublished a report in science, “what is the thermohaline circulation?,” in which he noted that the expressionhas been used in leading journals to signify at least seven different phenomena (circulation at the abyssal level,circulation driven by differences in density or buoyancy, “meridional overturning circulation of mass,” and soon)-though all have to do with ocean circulations and the transfer of heat, the cautiously vague and embracingsense in which i have employed it here.

north atlantic to the mid-pacific—but the volumes of heat and water they move are veryconsiderable, and the influence on the climate is enormous.

(as for the question of how anyone could possibly figure out how long it takes a drop ofwater to get from one ocean to another, the answer is that scientists can measure compoundsin the water like chlorofluorocarbons and work out how long it has been since they were lastin the air. by comparing a lot of measurements from different depths and locations they canreasonably chart the water’s movement.)thermohaline circulation not only moves heat around, but also helps to stir up nutrients asthe currents rise and fall, making greater volumes of the ocean habitable for fish and othermarine creatures. unfortunately, it appears the circulation may also be very sensitive tochange. according to computer simulations, even a modest dilution of the ocean’s saltcontent—from increased melting of the greenland ice sheet, for instance—could disrupt thecycle disastrously.

the seas do one other great favor for us. they soak up tremendous volumes of carbon andprovide a means for it to be safely locked away. one of the oddities of our solar system is thatthe sun burns about 25 percent more brightly now than when the solar system was young.

this should have resulted in a much warmer earth. indeed, as the english geologist aubreymanning has put it, “this colossal change should have had an absolutely catastrophic effecton the earth and yet it appears that our world has hardly been affected.”

so what keeps the world stable and cool?

life does. trillions upon trillions of tiny marine organisms that most of us have neverheard of—foraminiferans and coccoliths and calcareous algae—capture atmospheric carbon,in the form of carbon dioxide, when it falls as rain and use it (in combination with otherthings) to make their tiny shells. by locking the carbon up in their shells, they keep it frombeing reevaporated into the atmosphere, where it would build up dangerously as a greenhousegas. eventually all the tiny foraminiferans and coccoliths and so on die and fall to the bottomof the sea, where they are compressed into limestone. it is remarkable, when you behold anextraordinary natural feature like the white cliffs of dover in england, to reflect that it ismade up of nothing but tiny deceased marine organisms, but even more remarkable when yourealize how much carbon they cumulatively sequester. a six-inch cube of dover chalk willcontain well over a thousand liters of compressed carbon dioxide that would otherwise bedoing us no good at all. altogether there is about twenty thousand times as much carbonlocked away in the earth’s rocks as in the atmosphere. eventually much of that limestone willend up feeding volcanoes, and the carbon will return to the atmosphere and fall to the earth inrain, which is why the whole is called the long-term carbon cycle. the process takes a verylong time—about half a million years for a typical carbon atom—but in the absence of anyother disturbance it works remarkably well at keeping the climate stable.

unfortunately, human beings have a careless predilection for disrupting this cycle byputting lots of extra carbon into the atmosphere whether the foraminiferans are ready for it ornot. since 1850, it has been estimated, we have lofted about a hundred billion tons of extracarbon into the air, a total that increases by about seven billion tons each year. overall, that’snot actually all that much. nature—mostly through the belchings of volcanoes and the decayof plants—sends about 200 billion tons of carbon dioxide into the atmosphere each year,nearly thirty times as much as we do with our cars and factories. but you have only to look atthe haze that hangs over our cities to see what a difference our contribution makes.

we know from samples of very old ice that the “natural” level of carbon dioxide in theatmosphere—that is, before we started inflating it with industrial activity—is about 280 partsper million. by 1958, when people in lab coats started to pay attention to it, it had risen to 315parts per million. today it is over 360 parts per million and rising by roughly one-quarter of 1percent a year. by the end of the twenty-first century it is forecast to rise to about 560 partsper million.

so far, the earth’s oceans and forests (which also pack away a lot of carbon) have managedto save us from ourselves, but as peter cox of the british meteorological office puts it:

“there is a critical threshold where the natural biosphere stops buffering us from the effects ofour emissions and actually starts to amplify them.” the fear is that there would be a runawayincrease in the earth’s warming. unable to adapt, many trees and other plants would die,releasing their stores of carbon and adding to the problem. such cycles have occasionallyhappened in the distant past even without a human contribution. the good news is that evenhere nature is quite wonderful. it is almost certain that eventually the carbon cycle wouldreassert itself and return the earth to a situation of stability and happiness. the last time thishappened, it took a mere sixty thousand years.

18    THE BOUNDING MAIN

imagine trying to live in a world dominated by dihydrogen oxide, a compound that hasno taste or smell and is so variable in its properties that it is generally benign but at othertimes swiftly lethal. depending on its state, it can scald you or freeze you. in the presence ofcertain organic molecules it can form carbonic acids so nasty that they can strip the leavesfrom trees and eat the faces off statuary. in bulk, when agitated, it can strike with a fury thatno human edifice could withstand. even for those who have learned to live with it, it is anoften murderous substance. we call it water.

water is everywhere. a potato is 80 percent water, a cow 74 percent, a bacterium 75percent. a tomato, at 95 percent, is little but water. even humans are 65 percent water,making us more liquid than solid by a margin of almost two to one. water is strange stuff. it isformless and transparent, and yet we long to be beside it. it has no taste and yet we love thetaste of it. we will travel great distances and pay small fortunes to see it in sunshine. andeven though we know it is dangerous and drowns tens of thousands of people every year, wecan’t wait to frolic in it.

because water is so ubiquitous we tend to overlook what an extraordinary substance it is.

almost nothing about it can be used to make reliable predictions about the properties of otherliquids and vice versa. if you knew nothing of water and based your assumptions on thebehavior of compounds most chemically akin to it—hydrogen selenide or hydrogen sulphidenotably—you would expect it to boil at minus 135 degrees fahrenheit and to be a gas at roomtemperature.

most liquids when chilled contract by about 10 percent. water does too, but only down to apoint. once it is within whispering distance of freezing, it begins—perversely, beguilingly,extremely improbably—to expand. by the time it is solid, it is almost a tenth morevoluminous than it was before. because it expands, ice floats on water—“an utterly bizarreproperty,” according to john gribbin. if it lacked this splendid waywardness, ice would sink,and lakes and oceans would freeze from the bottom up. without surface ice to hold heat in,the water’s warmth would radiate away, leaving it even chillier and creating yet more ice.

soon even the oceans would freeze and almost certainly stay that way for a very long time,probably forever—hardly the conditions to nurture life. thankfully for us, water seemsunaware of the rules of chemistry or laws of physics.

everyone knows that water’s chemical formula is h2o, which means that it consists of onelargish oxygen atom with two smaller hydrogen atoms attached to it. the hydrogen atomscling fiercely to their oxygen host, but also make casual bonds with other water molecules.

the nature of a water molecule means that it engages in a kind of dance with other watermolecules, briefly pairing and then moving on, like the ever-changing partners in a quadrille,to use robert kunzig’s nice phrase. a glass of water may not appear terribly lively, but everymolecule in it is changing partners billions of times a second. that’s why water moleculesstick together to form bodies like puddles and lakes, but not so tightly that they can’t be easily
separated as when, for instance, you dive into a pool of them. at any given moment only 15percent of them are actually touching.

in one sense the bond is very strong—it is why water molecules can flow uphill whensiphoned and why water droplets on a car hood show such a singular determination to beadwith their partners. it is also why water has surface tension. the molecules at the surface areattracted more powerfully to the like molecules beneath and beside them than to the airmolecules above. this creates a sort of membrane strong enough to support insects andskipping stones. it is what gives the sting to a belly flop.

i hardly need point out that we would be lost without it. deprived of water, the human bodyrapidly falls apart. within days, the lips vanish “as if amputated, the gums blacken, the nosewithers to half its length, and the skin so contracts around the eyes as to prevent blinking.”

water is so vital to us that it is easy to overlook that all but the smallest fraction of the wateron earth is poisonous to us—deadly poisonous—because of the salts within it.

we need salt to live, but only in very small amounts, and seawater contains way more—about seventy times more—salt than we can safely metabolize. a typical liter of seawater willcontain only about 2.5 teaspoons of common salt—the kind we sprinkle on food—but muchlarger amounts of other elements, compounds, and other dissolved solids, which arecollectively known as salts. the proportions of these salts and minerals in our tissues isuncannily similar to seawater—we sweat and cry seawater, as margulis and sagan have putit—but curiously we cannot tolerate them as an input. take a lot of salt into your body andyour metabolism very quickly goes into crisis. from every cell, water molecules rush off likeso many volunteer firemen to try to dilute and carry off the sudden intake of salt. this leavesthe cells dangerously short of the water they need to carry out their normal functions. theybecome, in a word, dehydrated. in extreme situations, dehydration will lead to seizures,unconsciousness, and brain damage. meanwhile, the overworked blood cells carry the salt tothe kidneys, which eventually become overwhelmed and shut down. without functioningkidneys you die. that is why we don’t drink seawater.

there are 320 million cubic miles of water on earth and that is all we’re ever going to get.

the system is closed: practically speaking, nothing can be added or subtracted. the water youdrink has been around doing its job since the earth was young. by 3.8 billion years ago, theoceans had (at least more or less) achieved their present volumes.

the water realm is known as the hydrosphere and it is overwhelmingly oceanic. ninety-seven percent of all the water on earth is in the seas, the greater part of it in the pacific, whichcovers half the planet and is bigger than all the landmasses put together. altogether thepacific holds just over half of all the ocean water (51.6 percent to be precise); the atlantic has23.6 percent and the indian ocean 21.2 percent, leaving just 3.6 percent to be accounted forby all the other seas. the average depth of the ocean is 2.4 miles, with the pacific on averageabout a thousand feet deeper than the atlantic and indian oceans. altogether 60 percent ofthe planet’s surface is ocean more than a mile deep. as philip ball notes, we would better callour planet not earth but water.

of the 3 percent of earth’s water that is fresh, most exists as ice sheets. only the tiniestamount—0.036 percent—is found in lakes, rivers, and reservoirs, and an even smaller part—just 0.001 percent—exists in clouds or as vapor. nearly 90 percent of the planet’s ice is inantarctica, and most of the rest is in greenland. go to the south pole and you will bestanding on nearly two miles of ice, at the north pole just fifteen feet of it. antarctica alone
has six million cubic miles of ice—enough to raise the oceans by a height of two hundred feetif it all melted. but if all the water in the atmosphere fell as rain, evenly everywhere, theoceans would deepen by only an inch.

sea level, incidentally, is an almost entirely notional concept. seas are not level at all.

tides, winds, the coriolis force, and other effects alter water levels considerably from oneocean to another and within oceans as well. the pacific is about a foot and a half higher alongits western edge—a consequence of the centrifugal force created by the earth’s spin. just aswhen you pull on a tub of water the water tends to flow toward the other end, as if reluctant tocome with you, so the eastward spin of earth piles water up against the ocean’s westernmargins.

considering the age-old importance of the seas to us, it is striking how long it took theworld to take a scientific interest in them. until well into the nineteenth century most of whatwas known about the oceans was based on what washed ashore or came up in fishing nets,and nearly all that was written was based more on anecdote and supposition than on physicalevidence. in the 1830s, the british naturalist edward forbes surveyed ocean beds throughoutthe atlantic and mediterranean and declared that there was no life at all in the seas below2,000 feet. it seemed a reasonable assumption. there was no light at that depth, so no plantlife, and the pressures of water at such depths were known to be extreme. so it came assomething of a surprise when, in 1860, one of the first transatlantic telegraph cables washauled up for repairs from more than two miles down, and it was found to be thicklyencrusted with corals, clams, and other living detritus.

the first really organized investigation of the seas didn’t come until 1872, when a jointexpedition between the british museum, the royal society, and the british government setforth from portsmouth on a former warship called hms challenger. for three and a halfyears they sailed the world, sampling waters, netting fish, and hauling a dredge throughsediments. it was evidently dreary work. out of a complement of 240 scientists and crew, onein four jumped ship and eight more died or went mad—“driven to distraction by the mind-numbing routine of years of dredging” in the words of the historian samantha weinberg. butthey sailed across almost 70,000 nautical miles of sea, collected over 4,700 new species ofmarine organisms, gathered enough information to create a fifty-volume report (which tooknineteen years to put together), and gave the world the name of a new scientific discipline:

oceanography. they also discovered, by means of depth measurements, that there appeared tobe submerged mountains in the mid-atlantic, prompting some excited observers to speculatethat they had found the lost continent of atlantis.

because the institutional world mostly ignored the seas, it fell to devoted—and veryoccasional—amateurs to tell us what was down there. modern deep-water exploration beginswith charles william beebe and otis barton in 1930. although they were equal partners, themore colorful beebe has always received far more written attention. born in 1877 into a well-to-do family in new york city, beebe studied zoology at columbia university, then took ajob as a birdkeeper at the new york zoological society. tiring of that, he decided to adoptthe life of an adventurer and for the next quarter century traveled extensively through asiaand south america with a succession of attractive female assistants whose jobs wereinventively described as “historian and technicist” or “assistant in fish problems.” hesupported these endeavors with a succession of popular books with titles like edge of thejungle and jungle days, though he also produced some respectable books on wildlife andornithology.

in the mid-1920s, on a trip to the galápagos islands, he discovered “the delights ofdangling,” as he described deep-sea diving. soon afterward he teamed up with barton, whocame from an even wealthier family, had also attended columbia, and also longed foradventure. although beebe nearly always gets the credit, it was in fact barton who designedthe first bathysphere (from the greek word for “deep”) and funded the $12,000 cost of itsconstruction. it was a tiny and necessarily robust chamber, made of cast iron 1.5 inches thickand with two small portholes containing quartz blocks three inches thick. it held two men, butonly if they were prepared to become extremely well acquainted. even by the standards of theage, the technology was unsophisticated. the sphere had no maneuverability—it simply hungon the end of a long cable—and only the most primitive breathing system: to neutralize theirown carbon dioxide they set out open cans of soda lime, and to absorb moisture they opened asmall tub of calcium chloride, over which they sometimes waved palm fronds to encouragechemical reactions.

but the nameless little bathysphere did the job it was intended to do. on the first dive, injune 1930 in the bahamas, barton and beebe set a world record by descending to 600 feet. by1934, they had pushed the record to 3,028 feet, where it would stay until after the war. bartonwas confident the device was safe to a depth of 4,500 feet, though the strain on every bolt andrivet was audibly evident with each fathom they descended. at any depth, it was brave andrisky work. at 3,000 feet, their little porthole was subjected to nineteen tons of pressure persquare inch. death at such a depth would have been instantaneous, as beebe never failed toobserve in his many books, articles, and radio broadcasts. their main concern, however, wasthat the shipboard winch, straining to hold on to a metal ball and two tons of steel cable,would snap and send the two men plunging to the seafloor. in such an event, nothing couldhave saved them.

the one thing their descents didn’t produce was a great deal of worthwhile science.

although they encountered many creatures that had not been seen before, the limits ofvisibility and the fact that neither of the intrepid aquanauts was a trained oceanographer meantthey often weren’t able to describe their findings in the kind of detail that real scientistscraved. the sphere didn’t carry an external light, merely a 250-watt bulb they could hold upto the window, but the water below five hundred feet was practically impenetrable anyway,and they were peering into it through three inches of quartz, so anything they hoped to viewwould have to be nearly as interested in them as they were in it. about all they could report, inconsequence, was that there were a lot of strange things down there. on one dive in 1934,beebe was startled to spy a giant serpent “more than twenty feet long and very wide.” itpassed too swiftly to be more than a shadow. whatever it was, nothing like it has been seenby anyone since. because of such vagueness their reports were generally ignored byacademics.

after their record-breaking descent of 1934, beebe lost interest in diving and moved on toother adventures, but barton persevered. to his credit, beebe always told anyone who askedthat barton was the real brains behind the enterprise, but barton seemed unable to step fromthe shadows. he, too, wrote thrilling accounts of their underwater adventures and even starredin a hollywood movie called titans of the deep, featuring a bathysphere and many excitingand largely fictionalized encounters with aggressive giant squid and the like. he evenadvertised camel cigarettes (“they don’t give me jittery nerves”). in 1948 he increased thedepth record by 50 percent, with a dive to 4,500 feet in the pacific ocean near california, butthe world seemed determined to overlook him. one newspaper reviewer of titans of the deepactually thought the star of the film was beebe. nowadays, barton is lucky to get a mention.

at all events, he was about to be comprehensively eclipsed by a father-and-son team fromswitzerland, auguste and jacques piccard, who were designing a new type of probe called abathyscaphe (meaning “deep boat”). christened trieste, after the italian city in which it wasbuilt, the new device maneuvered independently, though it did little more than just go up anddown. on one of its first dives, in early 1954, it descended to below 13,287 feet, nearly threetimes barton’s record-breaking dive of six years earlier. but deep-sea dives required a greatdeal of costly support, and the piccards were gradually going broke.

in 1958, they did a deal with the u.s. navy, which gave the navy ownership but left themin control. now flush with funds, the piccards rebuilt the vessel, giving it walls five inchesthick and shrinking the windows to just two inches in diameter—little more than peepholes.

but it was now strong enough to withstand truly enormous pressures, and in january 1960jacques piccard and lieutenant don walsh of the u.s. navy sank slowly to the bottom of theocean’s deepest canyon, the mariana trench, some 250 miles off guam in the western pacific(and discovered, not incidentally, by harry hess with his fathometer). it took just under fourhours to fall 35,820 feet, or almost seven miles. although the pressure at that depth wasnearly 17,000 pounds per square inch, they noticed with surprise that they disturbed a bottom-dwelling flatfish just as they touched down. they had no facilities for taking photographs, sothere is no visual record of the event.

after just twenty minutes at the world’s deepest point, they returned to the surface. it wasthe only occasion on which human beings have gone so deep.

forty years later, the question that naturally occurs is: why has no one gone back since? tobegin with, further dives were vigorously opposed by vice admiral hyman g. rickover, aman who had a lively temperament, forceful views, and, most pertinently, control of thedepartmental checkbook. he thought underwater exploration a waste of resources and pointedout that the navy was not a research institute. the nation, moreover, was about to becomefully preoccupied with space travel and the quest to send a man to the moon, which madedeep sea investigations seem unimportant and rather old-fashioned. but the decisiveconsideration was that the trieste descent didn’t actually achieve much. as a navy officialexplained years later: “we didn’t learn a hell of a lot from it, other than that we could do it.

why do it again?” it was, in short, a long way to go to find a flatfish, and expensive too.

repeating the exercise today, it has been estimated, would cost at least $100 million.

when underwater researchers realized that the navy had no intention of pursuing apromised exploration program, there was a pained outcry. partly to placate its critics, thenavy provided funding for a more advanced submersible, to be operated by the woods holeoceanographic institution of massachusetts. called alvin, in somewhat contracted honor ofthe oceanographer allyn c. vine, it would be a fully maneuverable minisubmarine, though itwouldn’t go anywhere near as deep as the trieste. there was just one problem: the designerscouldn’t find anyone willing to build it. according to william j. broad in the universebelow: “no big company like general dynamics, which made submarines for the navy,wanted to take on a project disparaged by both the bureau of ships and admiral rickover, thegods of naval patronage.” eventually, not to say improbably, alvin was constructed bygeneral mills, the food company, at a factory where it made the machines to producebreakfast cereals.

as for what else was down there, people really had very little idea. well into the 1950s, thebest maps available to oceanographers were overwhelmingly based on a little detail fromscattered surveys going back to 1929 grafted onto, essentially an ocean of guesswork. the
navy had excellent charts with which to guide submarines through canyons and aroundguyots, but it didn’t wish such information to fall into soviet hands, so it kept its knowledgeclassified. academics therefore had to make do with sketchy and antiquated surveys or relyon hopeful surmise. even today our knowledge of the ocean floors remains remarkably lowresolution. if you look at the moon with a standard backyard telescope you will seesubstantial craters—fracastorious, blancanus, zach, planck, and many others familiar to anylunar scientist—that would be unknown if they were on our own ocean floors. we have bettermaps of mars than we do of our own seabeds.

at the surface level, investigative techniques have also been a trifle ad hoc. in 1994, thirty-four thousand ice hockey gloves were swept overboard from a korean cargo ship during astorm in the pacific. the gloves washed up all over, from vancouver to vietnam, helpingoceanographers to trace currents more accurately than they ever had before.

today alvin is nearly forty years old, but it still remains america’s premier research vessel.

there are still no submersibles that can go anywhere near the depth of the mariana trenchand only five, including alvin, that can reach the depths of the “abyssal plain”—the deepocean floor—that covers more than half the planet’s surface. a typical submersible costsabout $25,000 a day to operate, so they are hardly dropped into the water on a whim, still lessput to sea in the hope that they will randomly stumble on something of interest. it’s rather asif our firsthand experience of the surface world were based on the work of five guys exploringon garden tractors after dark. according to robert kunzig, humans may have scrutinized“perhaps a millionth or a billionth of the sea’s darkness. maybe less. maybe much less.”

but oceanographers are nothing if not industrious, and they have made several importantdiscoveries with their limited resources—including, in 1977, one of the most important andstartling biological discoveries of the twentieth century. in that year alvin found teemingcolonies of large organisms living on and around deep-sea vents off the galápagos islands—tube worms over ten feet long, clams a foot wide, shrimps and mussels in profusion,wriggling spaghetti worms. they all owed their existence to vast colonies of bacteria thatwere deriving their energy and sustenance from hydrogen sulfides—compounds profoundlytoxic to surface creatures—that were pouring steadily from the vents. it was a worldindependent of sunlight, oxygen, or anything else normally associated with life. this was aliving system based not on photosynthesis but on chemosynthesis, an arrangement thatbiologists would have dismissed as preposterous had anyone been imaginative enough tosuggest it.

huge amounts of heat and energy flow from these vents. two dozen of them together willproduce as much energy as a large power station, and the range of temperatures around themis enormous. the temperature at the point of outflow can be as much as 760 degreesfahrenheit, while a few feet away the water may be only two or three degrees above freezing.

a type of worm called an alvinellid was found living right on the margins, with the watertemperature 140 degrees warmer at its head than at its tail. before this it had been thought thatno complex organisms could survive in water warmer than about 130 degrees, and here wasone that was surviving warmer temperatures than that and extreme cold to boot. thediscovery transformed our understanding of the requirements for life.

it also answered one of the great puzzles of oceanography—something that many of usdidn’t realize was a puzzle—namely, why the oceans don’t grow saltier with time. at the riskof stating the obvious, there is a lot of salt in the sea—enough to bury every bit of land on theplanet to a depth of about five hundred feet. millions of gallons of fresh water evaporate from
the ocean daily, leaving all their salts behind, so logically the seas ought to grow more saltywith the passing years, but they don’t. something takes an amount of salt out of the waterequivalent to the amount being put in. for the longest time, no one could figure out whatcould be responsible for this.

alvin’s discovery of the deep-sea vents provided the answer. geophysicists realized that thevents were acting much like the filters in a fish tank. as water is taken down into the crust,salts are stripped from it, and eventually clean water is blown out again through the chimneystacks. the process is not swift—it can take up to ten million years to clean an ocean—but itis marvelously efficient as long as you are not in a hurry.

perhaps nothing speaks more clearly of our psychological remoteness from the oceandepths than that the main expressed goal for oceanographers during international geophysicalyear of 1957–58 was to study “the use of ocean depths for the dumping of radioactivewastes.” this wasn’t a secret assignment, you understand, but a proud public boast. in fact,though it wasn’t much publicized, by 1957–58 the dumping of radioactive wastes had alreadybeen going on, with a certain appalling vigor, for over a decade. since 1946, the united stateshad been ferrying fifty-five-gallon drums of radioactive gunk out to the farallon islands,some thirty miles off the california coast near san francisco, where it simply threw themoverboard.

it was all quite extraordinarily sloppy. most of the drums were exactly the sort you seerusting behind gas stations or standing outside factories, with no protective linings of anytype. when they failed to sink, which was usually, navy gunners riddled them with bullets tolet water in (and, of course, plutonium, uranium, and strontium out). before it was halted inthe 1990s, the united states had dumped many hundreds of thousands of drums into aboutfifty ocean sites—almost fifty thousand of them in the farallons alone. but the u.s. was by nomeans alone. among the other enthusiastic dumpers were russia, china, japan, new zealand,and nearly all the nations of europe.

and what effect might all this have had on life beneath the seas? well, little, we hope, butwe actually have no idea. we are astoundingly, sumptuously, radiantly ignorant of lifebeneath the seas. even the most substantial ocean creatures are often remarkably little knownto us—including the most mighty of them all, the great blue whale, a creature of suchleviathan proportions that (to quote david attenborough) its “tongue weighs as much as anelephant, its heart is the size of a car and some of its blood vessels are so wide that you couldswim down them.” it is the most gargantuan beast that earth has yet produced, bigger eventhan the most cumbrous dinosaurs. yet the lives of blue whales are largely a mystery to us.

much of the time we have no idea where they are—where they go to breed, for instance, orwhat routes they follow to get there. what little we know of them comes almost entirely fromeavesdropping on their songs, but even these are a mystery. blue whales will sometimes breakoff a song, then pick it up again at the same spot six months later. sometimes they strike upwith a new song, which no member can have heard before but which each already knows.

how they do this is not remotely understood. and these are animals that must routinely cometo the surface to breathe.

for animals that need never surface, obscurity can be even more tantalizing. consider thefabled giant squid. though nothing on the scale of the blue whale, it is a decidedly substantialanimal, with eyes the size of soccer balls and trailing tentacles that can reach lengths of sixty
feet. it weighs nearly a ton and is earth’s largest invertebrate. if you dumped one in a normalhousehold swimming pool, there wouldn’t be much room for anything else. yet no scientist—no person as far as we know—has ever seen a giant squid alive. zoologists have devotedcareers to trying to capture, or just glimpse, living giant squid and have always failed. theyare known mostly from being washed up on beaches—particularly, for unknown reasons, thebeaches of the south island of new zealand. they must exist in large numbers because theyform a central part of the sperm whale’s diet, and sperm whales take a lot of feeding.

1according to one estimate, there could be as many as thirty million species of animalsliving in the sea, most still undiscovered. the first hint of how abundant life is in the deepseas didn’t come until as recently as the 1960s with the invention of the epibenthic sled, adredging device that captures organisms not just on and near the seafloor but also buried inthe sediments beneath. in a single one-hour trawl along the continental shelf, at a depth of justunder a mile, woods hole oceanographers howard sandler and robert hessler netted over25,000 creatures—worms, starfish, sea cucumbers, and the like—representing 365 species.

even at a depth of three miles, they found some 3,700 creatures representing almost 200species of organism. but the dredge could only capture things that were too slow or stupid toget out of the way. in the late 1960s a marine biologist named john isaacs got the idea tolower a camera with bait attached to it, and found still more, in particular dense swarms ofwrithing hagfish, a primitive eel-like creature, as well as darting shoals of grenadier fish.

where a good food source is suddenly available—for instance, when a whale dies and sinks tothe bottom—as many as 390 species of marine creature have been found dining off it.

interestingly, many of these creatures were found to have come from vents up to a thousandmiles distant. these included such types as mussels and clams, which are hardly known asgreat travelers. it is now thought that the larvae of certain organisms may drift through thewater until, by some unknown chemical means, they detect that they have arrived at a foodopportunity and fall onto it.

so why, if the seas are so vast, do we so easily overtax them? well, to begin with, theworld’s seas are not uniformly bounteous. altogether less than a tenth of the ocean isconsidered naturally productive. most aquatic species like to be in shallow waters where thereis warmth and light and an abundance of organic matter to prime the food chain. coral reefs,for instance, constitute well under 1 percent of the ocean’s space but are home to about 25percent of its fish.

elsewhere, the oceans aren’t nearly so rich. take australia. with over 20,000 miles ofcoastline and almost nine million square miles of territorial waters, it has more sea lapping itsshores than any other country, yet, as tim flannery notes, it doesn’t even make it into the topfifty among fishing nations. indeed, australia is a large net importer of seafood. this isbecause much of australia’s waters are, like much of australia itself, essentially desert. (anotable exception is the great barrier reef off queensland, which is sumptuously fecund.)because the soil is poor, it produces little in the way of nutrient-rich runoff.

even where life thrives, it is often extremely sensitive to disturbance. in the 1970s, fishermenfrom australia and, to a lesser extent, new zealand discovered shoals of a little-known fishliving at a depth of about half a mile on their continental shelves. they were known as orange1the indigestible parts of giant squid, in particular their beaks, accumulate in sperm whales stomachs into thesubstance known as ambergris, which is used as a fixative in perfumes. the next time you spray on chanel no. 5(assuming you do), you may wish to reflect that you are dousing yourself in distillate of unseen sea monster.

roughy, they were delicious, and they existed in huge numbers. in no time at all, fishing fleetswere hauling in forty thousand metric tons of roughy a year. then marine biologists madesome alarming discoveries. roughy are extremely long lived and slow maturing. some maybe 150 years old; any roughy you have eaten may well have been born when victoria wasqueen. roughy have adopted this exceedingly unhurried lifestyle because the waters they livein are so resource-poor. in such waters, some fish spawn just once in a lifetime. clearly theseare populations that cannot stand a great deal of disturbance. unfortunately, by the time thiswas realized the stocks had been severely depleted. even with careful management it will bedecades before the populations recover, if they ever do.

elsewhere, however, the misuse of the oceans has been more wanton than inadvertent.

many fishermen “fin” sharks—that is, slice their fins off, then dump them back into the waterto die. in 1998, shark fins sold in the far east for over $250 a pound. a bowl of shark finsoup retailed in tokyo for $100. the world wildlife fund estimated in 1994 that the numberof sharks killed each year was between 40 million and 70 million.

as of 1995, some 37,000 industrial-sized fishing ships, plus about a million smaller boats,were between them taking twice as many fish from the sea as they had just twenty-five yearsearlier. trawlers are sometimes now as big as cruise ships and haul behind them nets bigenough to hold a dozen jumbo jets. some even use spotter planes to locate shoals of fish fromthe air.

it is estimated that about a quarter of every fishing net hauled up contains “by-catch”—fishthat can’t be landed because they are too small or of the wrong type or caught in the wrongseason. as one observer told the economist: “we’re still in the dark ages. we just drop a netdown and see what comes up.” perhaps as much as twenty-two million metric tons of suchunwanted fish are dumped back in the sea each year, mostly in the form of corpses. for everypound of shrimp harvested, about four pounds of fish and other marine creatures aredestroyed.

large areas of the north sea floor are dragged clean by beam trawlers as many as seventimes a year, a degree of disturbance that no ecosystem can withstand. at least two-thirds ofspecies in the north sea, by many estimates, are being overfished. across the atlantic thingsare no better. halibut once abounded in such numbers off new england that individual boatscould land twenty thousand pounds of it in a day. now halibut is all but extinct off thenortheast coast of north america.

nothing, however, compares with the fate of cod. in the late fifteenth century, the explorerjohn cabot found cod in incredible numbers on the eastern banks of north america—shallowareas of water popular with bottom-feeding fish like cod. some of these banks were vast.

georges banks off massachusetts is bigger than the state it abuts. the grand banks offnewfoundland is bigger still and for centuries was always dense with cod. they were thoughtto be inexhaustible. of course they were anything but.

by 1960, the number of spawning cod in the north atlantic had fallen to an estimated 1.6million metric tons. by 1990 this had sunk to 22,000 metric tons. in commercial terms, thecod were extinct. “fishermen,” wrote mark kurlansky in his fascinating history, cod, “hadcaught them all.” the cod may have lost the western atlantic forever. in 1992, cod fishingwas stopped altogether on the grand banks, but as of last autumn, according to a report innature, stocks had not staged a comeback. kurlansky notes that the fish of fish fillets and fish
sticks was originally cod, but then was replaced by haddock, then by redfish, and lately bypacific pollock. these days, he notes drily, “fish” is “whatever is left.”

much the same can be said of many other seafoods. in the new england fisheries offrhode island, it was once routine to haul in lobsters weighing twenty pounds. sometimes theyreached thirty pounds. left unmolested, lobsters can live for decades—as much as seventyyears, it is thought—and they never stop growing. nowadays few lobsters weigh more thantwo pounds on capture. “biologists,” according to the new york times, “estimate that 90percent of lobsters are caught within a year after they reach the legal minimum size at aboutage six.” despite declining catches, new england fishermen continue to receive state andfederal tax incentives that encourage them—in some cases all but compel them—to acquirebigger boats and to harvest the seas more intensively. today fishermen of massachusetts arereduced to fishing the hideous hagfish, for which there is a slight market in the far east, buteven their numbers are now falling.

we are remarkably ignorant of the dynamics that rule life in the sea. while marine life ispoorer than it ought to be in areas that have been overfished, in some naturally impoverishedwaters there is far more life than there ought to be. the southern oceans around antarcticaproduce only about 3 percent of the world’s phytoplankton—far too little, it would seem, tosupport a complex ecosystem, and yet it does. crab-eater seals are not a species of animal thatmost of us have heard of, but they may actually be the second most numerous large species ofanimal on earth, after humans. as many as fifteen million of them may live on the pack icearound antarctica. there are also perhaps two million weddel seals, at least half a millionemperor penguins, and maybe as many as four million adélie penguins. the food chain isthus hopelessly top heavy, but somehow it works. remarkably no one knows how.

all this is a very roundabout way of making the point that we know very little about earth’sbiggest system. but then, as we shall see in the pages remaining to us, once you start talkingabout life, there is a great deal we don’t know, not least how it got going in the first place.

19    THE RISE OF LIFE

in 1953, stanley miller, a graduate student at the university of chicago, took twoflasks—one containing a little water to represent a primeval ocean, the other holding amixture of methane, ammonia, and hydrogen sulphide gases to represent earth’s earlyatmosphere—connected them with rubber tubes, and introduced some electrical sparks as astand-in for lightning. after a few days, the water in the flasks had turned green and yellow ina hearty broth of amino acids, fatty acids, sugars, and other organic compounds. “if goddidn’t do it this way,” observed miller’s delighted supervisor, the nobel laureate haroldurey, “he missed a good bet.”

press reports of the time made it sound as if about all that was needed now was forsomebody to give the whole a good shake and life would crawl out. as time has shown, itwasn’t nearly so simple. despite half a century of further study, we are no nearer tosynthesizing life today than we were in 1953 and much further away from thinking we can.

scientists are now pretty certain that the early atmosphere was nothing like as primed fordevelopment as miller and urey’s gaseous stew, but rather was a much less reactive blend ofnitrogen and carbon dioxide. repeating miller’s experiments with these more challenginginputs has so far produced only one fairly primitive amino acid. at all events, creating aminoacids is not really the problem. the problem is proteins.

proteins are what you get when you string amino acids together, and we need a lot of them.

no one really knows, but there may be as many as a million types of protein in the humanbody, and each one is a little miracle. by all the laws of probability proteins shouldn’t exist.

to make a protein you need to assemble amino acids (which i am obliged by long tradition torefer to here as “the building blocks of life”) in a particular order, in much the same way thatyou assemble letters in a particular order to spell a word. the problem is that words in theamino acid alphabet are often exceedingly long. to spell collagen, the name of a commontype of protein, you need to arrange eight letters in the right order. but to make collagen, youneed to arrange 1,055 amino acids in precisely the right sequence. but—and here’s anobvious but crucial point—you don’t make it. it makes itself, spontaneously, withoutdirection, and this is where the unlikelihoods come in.

the chances of a 1,055-sequence molecule like collagen spontaneously self-assembling are,frankly, nil. it just isn’t going to happen. to grasp what a long shot its existence is, visualize astandard las vegas slot machine but broadened greatly—to about ninety feet, to be precise—to accommodate 1,055 spinning wheels instead of the usual three or four, and with twentysymbols on each wheel (one for each common amino acid).

1how long would you have topull the handle before all 1,055 symbols came up in the right order? effectively forever. evenif you reduced the number of spinning wheels to two hundred, which is actually a moretypical number of amino acids for a protein, the odds against all two hundred coming up in a1there are actually twenty-two naturally occurring amino acids known on earth, and more may await discovery,but only twenty of them are necessary to produce us and most other living things. the twenty-second, calledpyrrolysine, was discovered in 2002 by researchers at ohio state university and is found only in a single type ofarchaean (a basic form of life that we will discuss a little further on in the story) called methanosarcina barkeri.

prescribed sequence are 1 in 10260(that is a 1 followed by 260 zeroes). that in itself is a largernumber than all the atoms in the universe.

proteins, in short, are complex entities. hemoglobin is only 146 amino acids long, a runt byprotein standards, yet even it offers 10190possible amino acid combinations, which is why ittook the cambridge university chemist max perutz twenty-three years—a career, more orless—to unravel it. for random events to produce even a single protein would seem astunning improbability—like a whirlwind spinning through a junkyard and leaving behind afully assembled jumbo jet, in the colorful simile of the astronomer fred hoyle.

yet we are talking about several hundred thousand types of protein, perhaps a million, eachunique and each, as far as we know, vital to the maintenance of a sound and happy you. andit goes on from there. a protein to be of use must not only assemble amino acids in the rightsequence, but then must engage in a kind of chemical origami and fold itself into a veryspecific shape. even having achieved this structural complexity, a protein is no good to you ifit can’t reproduce itself, and proteins can’t. for this you need dna. dna is a whiz atreplicating—it can make a copy of itself in seconds—but can do virtually nothing else. so wehave a paradoxical situation. proteins can’t exist without dna, and dna has no purposewithout proteins. are we to assume then that they arose simultaneously with the purpose ofsupporting each other? if so: wow.

and there is more still. dna, proteins, and the other components of life couldn’t prosperwithout some sort of membrane to contain them. no atom or molecule has ever achieved lifeindependently. pluck any atom from your body, and it is no more alive than is a grain of sand.

it is only when they come together within the nurturing refuge of a cell that these diversematerials can take part in the amazing dance that we call life. without the cell, they arenothing more than interesting chemicals. but without the chemicals, the cell has no purpose.

as the physicist paul davies puts it, “if everything needs everything else, how did thecommunity of molecules ever arise in the first place?” it is rather as if all the ingredients inyour kitchen somehow got together and baked themselves into a cake—but a cake that couldmoreover divide when necessary to produce more cakes. it is little wonder that we call it themiracle of life. it is also little wonder that we have barely begun to understand it.

so what accounts for all this wondrous complexity? well, one possibility is that perhaps itisn’t quite—not quite—so wondrous as at first it seems. take those amazingly improbableproteins. the wonder we see in their assembly comes in assuming that they arrived on thescene fully formed. but what if the protein chains didn’t assemble all at once? what if, in thegreat slot machine of creation, some of the wheels could be held, as a gambler might hold anumber of promising cherries? what if, in other words, proteins didn’t suddenly burst intobeing, but evolved .

imagine if you took all the components that make up a human being—carbon, hydrogen,oxygen, and so on—and put them in a container with some water, gave it a vigorous stir, andout stepped a completed person. that would be amazing. well, that’s essentially what hoyleand others (including many ardent creationists) argue when they suggest that proteinsspontaneously formed all at once. they didn’t—they can’t have. as richard dawkins arguesin the blind watchmaker, there must have been some kind of cumulative selection processthat allowed amino acids to assemble in chunks. perhaps two or three amino acids linked up
for some simple purpose and then after a time bumped into some other similar small clusterand in so doing “discovered” some additional improvement.

chemical  reactions  of  the  sort  associated with life are actually something of acommonplace. it may be beyond us to cook them up in a lab, à la stanley miller and haroldurey, but the universe does it readily enough. lots of molecules in nature get together to formlong chains called polymers. sugars constantly assemble to form starches. crystals can do anumber of lifelike things—replicate, respond to environmental stimuli, take on a patternedcomplexity. they’ve never achieved life itself, of course, but they demonstrate repeatedly thatcomplexity is a natural, spontaneous, entirely commonplace event. there may or may not be agreat deal of life in the universe at large, but there is no shortage of ordered self-assembly, ineverything from the transfixing symmetry of snowflakes to the comely rings of saturn.

so powerful is this natural impulse to assemble that many scientists now believe that lifemay be more inevitable than we think—that it is, in the words of the belgian biochemist andnobel laureate christian de duve, “an obligatory manifestation of matter, bound to arisewherever conditions are appropriate.” de duve thought it likely that such conditions would beencountered perhaps a million times in every galaxy.

certainly there is nothing terribly exotic in the chemicals that animate us. if you wished tocreate another living object, whether a goldfish or a head of lettuce or a human being, youwould need really only four principal elements, carbon, hydrogen, oxygen, and nitrogen, plussmall amounts of a few others, principally sulfur, phosphorus, calcium, and iron. put thesetogether in three dozen or so combinations to form some sugars, acids, and other basiccompounds and you can build anything that lives. as dawkins notes: “there is nothingspecial about the substances from which living things are made. living things are collectionsof molecules, like everything else.”

the bottom line is that life is amazing and gratifying, perhaps even miraculous, but hardlyimpossible—as we repeatedly attest with our own modest existences. to be sure, many of thedetails of life’s beginnings remain pretty imponderable. every scenario you have ever readconcerning the conditions necessary for life involves water—from the “warm little pond”

where darwin supposed life began to the bubbling sea vents that are now the most popularcandidates for life’s beginnings—but all this overlooks the fact that to turn monomers intopolymers (which is to say, to begin to create proteins) involves what is known to biology as“dehydration linkages.” as one leading biology text puts it, with perhaps just a tiny hint ofdiscomfort, “researchers agree that such reactions would not have been energeticallyfavorable in the primitive sea, or indeed in any aqueous medium, because of the mass actionlaw.” it is a little like putting sugar in a glass of water and having it become a cube. itshouldn’t happen, but somehow in nature it does. the actual chemistry of all this is a littlearcane for our purposes here, but it is enough to know that if you make monomers wet theydon’t turn into polymers—except when creating life on earth. how and why it happens thenand not otherwise is one of biology’s great unanswered questions.

one of the biggest surprises in the earth sciences in recent decades was the discovery ofjust how early in earth’s history life arose. well into the 1950s, it was thought that life wasless than 600 million years old. by the 1970s, a few adventurous souls felt that maybe it wentback 2.5 billion years. but the present date of 3.85 billion years is stunningly early. earth’ssurface didn’t become solid until about 3.9 billion years ago.

“we can only infer from this rapidity that it is not ‘difficult’ for life of bacterial grade toevolve on planets with appropriate conditions,” stephen jay gould observed in the new yorktimes in 1996. or as he put it elsewhere, it is hard to avoid the conclusion that “life, arising assoon as it could, was chemically destined to be.”

life emerged so swiftly, in fact, that some authorities think it must have had help—perhapsa good deal of help. the idea that earthly life might have arrived from space has a surprisinglylong and even occasionally distinguished history. the great lord kelvin himself raised thepossibility as long ago as 1871 at a meeting of the british association for the advancement ofscience when he suggested that “the germs of life might have been brought to the earth bysome meteorite.” but it remained little more than a fringe notion until one sunday inseptember 1969 when tens of thousands of australians were startled by a series of sonicbooms and the sight of a fireball streaking from east to west across the sky. the fireball madea strange crackling sound as it passed and left behind a smell that some likened to methylatedspirits and others described as just awful.

the fireball exploded above murchison, a town of six hundred people in the goulburnvalley north of melbourne, and came raining down in chunks, some weighing up to twelvepounds. fortunately, no one was hurt. the meteorite was of a rare type known as acarbonaceous chondrite, and the townspeople helpfully collected and brought in some twohundred pounds of it. the timing could hardly have been better. less than two months earlier,the apollo 11 astronauts had returned to earth with a bag full of lunar rocks, so labsthroughout the world were geared up—indeed clamoring—for rocks of extraterrestrial origin.

the murchison meteorite was found to be 4.5 billion years old, and it was studded withamino acids—seventy-four types in all, eight of which are involved in the formation of earthlyproteins. in late 2001, more than thirty years after it crashed, a team at the ames researchcenter in california announced that the murchison rock also contained complex strings ofsugars called polyols, which had not been found off the earth before.

a few other carbonaceous chondrites have strayed into earth’s path since—one that landednear tagish lake in canada’s yukon in january 2000 was seen over large parts of northamerica—and they have likewise confirmed that the universe is actually rich in organiccompounds. halley’s comet, it is now thought, is about 25 percent organic molecules. getenough of those crashing into a suitable place—earth, for instance—and you have the basicelements you need for life.

there are two problems with notions of panspermia, as extraterrestrial theories are known.

the first is that it doesn’t answer any questions about how life arose, but merely movesresponsibility for it elsewhere. the other is that panspermia sometimes excites even the mostrespectable adherents to levels of speculation that can be safely called imprudent. franciscrick, codiscoverer of the structure of dna, and his colleague leslie orgel have suggestedthat earth was “deliberately seeded with life by intelligent aliens,” an idea that gribbin calls“at the very fringe of scientific respectability”—or, put another way, a notion that would beconsidered wildly lunatic if not voiced by a nobel laureate. fred hoyle and his colleaguechandra wickramasinghe further eroded enthusiasm for panspermia by suggesting that outerspace brought us not only life but also many diseases such as flu and bubonic plague, ideasthat were easily disproved by biochemists. hoyle—and it seems necessary to insert areminder here that he was one of the great scientific minds of the twentieth century—alsoonce suggested, as mentioned earlier, that our noses evolved with the nostrils underneath as away of keeping cosmic pathogens from falling into them as they drifted down from space.

whatever prompted life to begin, it happened just once. that is the most extraordinary factin biology, perhaps the most extraordinary fact we know. everything that has ever lived, plantor animal, dates its beginnings from the same primordial twitch. at some point in anunimaginably distant past some little bag of chemicals fidgeted to life. it absorbed somenutrients, gently pulsed, had a brief existence. this much may have happened before, perhapsmany times. but this ancestral packet did something additional and extraordinary: it cleaveditself and produced an heir. a tiny bundle of genetic material passed from one living entity toanother, and has never stopped moving since. it was the moment of creation for us all.

biologists sometimes call it the big birth.

“wherever you go in the world, whatever animal, plant, bug, or blob you look at, if it isalive, it will use the same dictionary and know the same code. all life is one,” says mattridley. we are all the result of a single genetic trick handed down from generation togeneration nearly four billion years, to such an extent that you can take a fragment of humangenetic instruction, patch it into a faulty yeast cell, and the yeast cell will put it to work as if itwere its own. in a very real sense, it is its own.

the dawn of life—or something very like it—sits on a shelf in the office of a friendlyisotope geochemist named victoria bennett in the earth sciences building of the australiannational university in canberra. an american, ms. bennett came to the anu fromcalifornia on a two-year contract in 1989 and has been there ever since. when i visited her, inlate 2001, she handed me a modestly hefty hunk of rock composed of thin alternating stripesof white quartz and a gray-green material called clinopyroxene. the rock came from akiliaisland in greenland, where unusually ancient rocks were found in 1997. the rocks are 3.85billion years old and represent the oldest marine sediments ever found.

“we can’t be certain that what you are holding once contained living organisms becauseyou’d have to pulverize it to find out,” bennett told me. “but it comes from the same depositwhere the oldest life was excavated, so it probably had life in it.” nor would you find actualfossilized microbes, however carefully you searched. any simple organisms, alas, would havebeen baked away by the processes that turned ocean mud to stone. instead what we would seeif we crunched up the rock and examined it microscopically would be the chemical residuesthat the organisms left behind—carbon isotopes and a type of phosphate called apatite, whichtogether provide strong evidence that the rock once contained colonies of living things. “wecan only guess what the organism might have looked like,” bennett said. “it was probablyabout as basic as life can get—but it was life nonetheless. it lived. it propagated.”

and eventually it led to us.

if you are into very old rocks, and bennett indubitably is, the anu has long been a primeplace to be. this is largely thanks to the ingenuity of a man named bill compston, who isnow retired but in the 1970s built the world’s first sensitive high resolution ion microprobe—or shrimp, as it is more affectionately known from its initial letters. this is amachine that measures the decay rate of uranium in tiny minerals called zircons. zirconsappear in most rocks apart from basalts and are extremely durable, surviving every naturalprocess but subduction. most of the earth’s crust has been slipped back into the oven at somepoint, but just occasionally—in western australia and greenland, for example—geologistshave found outcrops of rocks that have remained always at the surface. compston’s machineallowed such rocks to be dated with unparalleled precision. the prototype shrimp was built
and machined in the earth science department’s own workshops, and looked like somethingthat had been built from spare parts on a budget, but it worked great. on its first formal test, in1982, it dated the oldest thing ever found—a 4.3-billion-year-old  rock from westernaustralia.

“it caused quite a stir at the time,” bennett told me, “to find something so important soquickly with brand-new technology.”

she took me down the hall to see the current model, shrimp ii. it was a big heavy pieceof stainless-steel apparatus, perhaps twelve feet long and five feet high, and as solidly built asa deep-sea probe. at a console in front of it, keeping an eye on ever-changing strings offigures on a screen, was a man named bob from canterbury university in new zealand. hehad been there since 4 a.m., he told me. shrimp ii runs twenty-four hours a day; there’s thatmany rocks to date. it was just after 9a.m. and bob had the machine till noon. ask a pair ofgeochemists how something like this works, and they will start talking about isotopicabundances and ionization levels with an enthusiasm that is more endearing than fathomable.

the upshot of it, however, was that the machine, by bombarding a sample of rock withstreams of charged atoms, is able to detect subtle differences in the amounts of lead anduranium in the zircon samples, by which means the age of rocks can be accurately adduced.

bob told me that it takes about seventeen minutes to read one zircon and it is necessary toread dozens from each rock to make the data reliable. in practice, the process seemed toinvolve about the same level of scattered activity, and about as much stimulation, as a trip to alaundromat. bob seemed very happy, however; but then people from new zealand verygenerally do.

the earth sciences compound was an odd combination of things—part offices, part labs,part machine shed. “we used to build everything here,” bennett said. “we even had our ownglassblower, but he’s retired. but we still have two full-time rock crushers.” she caught mylook of mild surprise. “we get through a lot of rocks. and they have to be very carefullyprepared. you have to make sure there is no contamination from previous samples—no dustor anything. it’s quite a meticulous process.” she showed me the rock-crushing machines,which were indeed pristine, though the rock crushers had apparently gone for coffee. besidethe machines were large boxes containing rocks of all shapes and sizes. they do indeed getthrough a lot of rocks at the anu.

back in bennett’s office after our tour, i noticed hanging on her wall a poster giving anartist’s colorfully imaginative interpretation of earth as it might have looked 3.5 billion yearsago, just when life was getting going, in the ancient period known to earth science as thearchaean. the poster showed an alien landscape of huge, very active volcanoes, and asteamy, copper-colored sea beneath a harsh red sky. stromatolites, a kind of bacterial rock,filled the shallows in the foreground. it didn’t look like a very promising place to create andnurture life. i asked her if the painting was accurate.

“well, one school of thought says it was actually cool then because the sun was muchweaker.” (i later learned that biologists, when they are feeling jocose, refer to this as the“chinese restaurant problem”—because we had a dim sun.) “without an atmosphereultraviolet rays from the sun, even from a weak sun, would have tended to break apart anyincipient bonds made by molecules. and yet right there”—she tapped the stromatolites—“youhave organisms almost at the surface. it’s a puzzle.”

“so we don’t know what the world was like back then?”

“mmmm,” she agreed thoughtfully.

“either way it doesn’t seem very conducive to life.”

she nodded amiably. “but there must have been something that suited life. otherwise wewouldn’t be here.”

it certainly wouldn’t have suited us. if you were to step from a time machine into thatancient archaean world, you would very swiftly scamper back inside, for there was no moreoxygen to breathe on earth back then than there is on mars today. it was also full of noxiousvapors from hydrochloric and sulfuric acids powerful enough to eat through clothing andblister skin. nor would it have provided the clean and glowing vistas depicted in the poster invictoria bennett’s office. the chemical stew that was the atmosphere then would haveallowed little sunlight to reach the earth’s surface. what little you could see would beillumined only briefly by bright and frequent lightning flashes. in short, it was earth, but anearth we wouldn’t recognize as our own.

anniversaries were few and far between in the archaean world. for two billion yearsbacterial organisms were the only forms of life. they lived, they reproduced, they swarmed,but they didn’t show any particular inclination to move on to another, more challenging levelof existence. at some point in the first billion years of life, cyanobacteria, or blue-green algae,learned to tap into a freely available resource—the hydrogen that exists in spectacularabundance in water. they absorbed water molecules, supped on the hydrogen, and releasedthe oxygen as waste, and in so doing invented photosynthesis. as margulis and sagan note,photosynthesis is “undoubtedly the most important single metabolic innovation in the historyof life on the planet”—and it was invented not by plants but by bacteria.

as cyanobacteria proliferated the world began to fill with o2to the consternation of thoseorganisms that found it poisonous—which in those days was all of them. in an anaerobic (or anon-oxygen-using) world, oxygen is extremely poisonous. our white cells actually useoxygen to kill invading bacteria. that oxygen is fundamentally toxic often comes as a surpriseto those of us who find it so convivial to our well-being, but that is only because we haveevolved to exploit it. to other things it is a terror. it is what turns butter rancid and makes ironrust. even we can tolerate it only up to a point. the oxygen level in our cells is only about atenth the level found in the atmosphere.

the new oxygen-using organisms had two advantages. oxygen was a more efficient way toproduce energy, and it vanquished competitor organisms. some retreated into the oozy,anaerobic world of bogs and lake bottoms. others did likewise but then later (much later)migrated to the digestive tracts of beings like you and me. quite a number of these primevalentities are alive inside your body right now, helping to digest your food, but abhorring eventhe tiniest hint of o2. untold numbers of others failed to adapt and died.

the cyanobacteria were a runaway success. at first, the extra oxygen they produced didn’taccumulate in the atmosphere, but combined with iron to form ferric oxides, which sank to thebottom of primitive seas. for millions of years, the world literally rusted—a phenomenonvividly recorded in the banded iron deposits that provide so much of the world’s iron oretoday. for many tens of millions of years not a great deal more than this happened. if youwent back to that early proterozoic world you wouldn’t find many signs of promise for
earth’s future life. perhaps here and there in sheltered pools you’d encounter a film of livingscum or a coating of glossy greens and browns on shoreline rocks, but otherwise life remainedinvisible.

but about 3.5 billion years ago something more emphatic became apparent. wherever theseas were shallow, visible structures began to appear. as they went through their chemicalroutines, the cyanobacteria became very slightly tacky, and that tackiness trappedmicroparticles of dust and sand, which became bound together to form slightly weird but solidstructures—the stromatolites that were featured in the shallows of the poster on victoriabennett’s office wall. stromatolites came in various shapes and sizes. sometimes they lookedlike enormous cauliflowers, sometimes like fluffy mattresses (stromatolite comes from thegreek for “mattress”), sometimes they came in the form of columns, rising tens of metersabove the surface of the water—sometimes as high as a hundred meters. in all theirmanifestations, they were a kind of living rock, and they represented the world’s firstcooperative venture, with some varieties of primitive organism living just at the surface andothers living just underneath, each taking advantage of conditions created by the other. theworld had its first ecosystem.

for many years, scientists knew about stromatolites from fossil formations, but in 1961they got a real surprise with the discovery of a community of living stromatolites at sharkbay on the remote northwest coast of australia. this was most unexpected—so unexpected,in fact, that it was some years before scientists realized quite what they had found. today,however, shark bay is a tourist attraction—or at least as much of a tourist attraction as a placehundreds of miles from anywhere much and dozens of miles from anywhere at all can ever be.

boardwalks have been built out into the bay so that visitors can stroll over the water to get agood look at the stromatolites, quietly respiring just beneath the surface. they are lusterlessand gray and look, as i recorded in an earlier book, like very large cow-pats. but it is acuriously giddying moment to find yourself staring at living remnants of earth as it was 3.5billion years ago. as richard fortey has put it: “this is truly time traveling, and if the worldwere attuned to its real wonders this sight would be as well-known as the pyramids of giza.”

although you’d never guess it, these dull rocks swarm with life, with an estimated (well,obviously estimated) three billion individual organisms on every square yard of rock.

sometimes when you look carefully you can see tiny strings of bubbles rising to the surface asthey give up their oxygen. in two billion years such tiny exertions raised the level of oxygenin earth’s atmosphere to 20 percent, preparing the way for the next, more complex chapter inlife’s history.

it has been suggested that the cyanobacteria at shark bay are perhaps the slowest-evolvingorganisms on earth, and certainly now they are among the rarest. having prepared the way formore complex life forms, they were then grazed out of existence nearly everywhere by thevery organisms whose existence they had made possible. (they exist at shark bay becausethe waters are too saline for the creatures that would normally feast on them.)one reason life took so long to grow complex was that the world had to wait until thesimpler organisms had oxygenated the atmosphere sufficiently. “animals could not summonup the energy to work,” as fortey has put it. it took about two billion years, roughly 40percent of earth’s history, for oxygen levels to reach more or less modern levels ofconcentration in the atmosphere. but once the stage was set, and apparently quite suddenly, anentirely new type of cell arose—one with a nucleus and other little bodies collectively calledorganelles (from a greek word meaning “little tools”). the process is thought to have startedwhen some blundering or adventuresome bacterium either invaded or was captured by some
other bacterium and it turned out that this suited them both. the captive bacterium became, itis thought, a mitochondrion. this mitochondrial invasion (or endosymbiotic event, asbiologists like to term it) made complex life possible. (in plants a similar invasion producedchloroplasts, which enable plants to photosynthesize.)mitochondria manipulate oxygen in a way that liberates energy from foodstuffs. withoutthis niftily facilitating trick, life on earth today would be nothing more than a sludge ofsimple microbes. mitochondria are very tiny—you could pack a billion into the spaceoccupied by a grain of sand—but also very hungry. almost every nutriment you absorb goesto feeding them.

we couldn’t live for two minutes without them, yet even after a billion years mitochondriabehave as if they think things might not work out between us. they maintain their own dna.

they reproduce at a different time from their host cell. they look like bacteria, divide likebacteria, and sometimes respond to antibiotics in the way bacteria do. in short, they keep theirbags packed. they don’t even speak the same genetic language as the cell in which they live.

it is like having a stranger in your house, but one who has been there for a billion years.

the new type of cell is known as a eukaryote (meaning “truly nucleated”), as contrastedwith the old type, which is known as a prokaryote (“prenucleated”), and it seems to havearrived suddenly in the fossil record. the oldest eukaryotes yet known, called grypania, werediscovered in iron sediments in michigan in 1992. such fossils have been found just once, andthen no more are known for 500 million years.

compared with the new eukaryotes the old prokaryotes were little more than “bags ofchemicals,” in the words of the geologist stephen drury. eukaryotes were bigger—eventuallyas much as ten thousand times bigger—than their simpler cousins, and carried as much as athousand times more dna. gradually a system evolved in which life was dominated by twotypes of form—organisms that expel oxygen (like plants) and those that take it in (you andme).

single-celled eukaryotes were once called protozoa (“pre-animals”), but that term isincreasingly disdained. today the common term for them is protists . compared with thebacteria that had gone before, these new protists were wonders of design and sophistication.

the simple amoeba, just one cell big and without any ambitions but to exist, contains 400million bits of genetic information in its dna—enough, as carl sagan noted, to fill eightybooks of five hundred pages.

eventually the eukaryotes learned an even more singular trick. it took a long time—abillion years or so—but it was a good one when they mastered it. they learned to formtogether into complex multicellular beings. thanks to this innovation, big, complicated,visible entities like us were possible. planet earth was ready to move on to its next ambitiousphase.

but before we get too excited about that, it is worth remembering that the world, as we areabout to see, still belongs to the very small.

20    SMALL WORLD

it’s probably not a good idea to take too personal an interest in your microbes. louispasteur, the great french chemist and bacteriologist, became so preoccupied with them that hetook to peering critically at every dish placed before him with a magnifying glass, a habit thatpresumably did not win him many repeat invitations to dinner.

in fact, there is no point in trying to hide from your bacteria, for they are on and around youalways, in numbers you can’t conceive. if you are in good health and averagely diligent abouthygiene, you will have a herd of about one trillion bacteria grazing on your fleshy plains—about a hundred thousand of them on every square centimeter of skin. they are there to dineoff the ten billion or so flakes of skin you shed every day, plus all the tasty oils and fortifyingminerals that seep out from every pore and fissure. you are for them the ultimate food court,with the convenience of warmth and constant mobility thrown in. by way of thanks, they giveyou b.o.

and those are just the bacteria that inhabit your skin. there are trillions more tucked awayin your gut and nasal passages, clinging to your hair and eyelashes, swimming over thesurface of your eyes, drilling through the enamel of your teeth. your digestive system alone ishost to more than a hundred trillion microbes, of at least four hundred types. some deal withsugars, some with starches, some attack other bacteria. a surprising number, like theubiquitous intestinal spirochetes, have no detectable function at all. they just seem to like tobe with you. every human body consists of about 10 quadrillion cells, but about 100quadrillion bacterial cells. they are, in short, a big part of us. from the bacteria’s point ofview, of course, we are a rather small part of them.

because we humans are big and clever enough to produce and utilize antibiotics anddisinfectants, it is easy to convince ourselves that we have banished bacteria to the fringes ofexistence. don’t you believe it. bacteria may not build cities or have interesting social lives,but they will be here when the sun explodes. this is their planet, and we are on it onlybecause they allow us to be.

bacteria, never forget, got along for billions of years without us. we couldn’t survive a daywithout them. they process our wastes and make them usable again; without their diligentmunching nothing would rot. they purify our water and keep our soils productive. bacteriasynthesize vitamins in our gut, convert the things we eat into useful sugars andpolysaccharides, and go to war on alien microbes that slip down our gullet.

we depend totally on bacteria to pluck nitrogen from the air and convert it into usefulnucleotides and amino acids for us. it is a prodigious and gratifying feat. as margulis andsagan note, to do the same thing industrially (as when making fertilizers) manufacturers mustheat the source materials to 500 degrees centigrade and squeeze them to three hundred timesnormal pressures. bacteria do it all the time without fuss, and thank goodness, for no larger
organism could survive without the nitrogen they pass on. above all, microbes continue toprovide us with the air we breathe and to keep the atmosphere stable. microbes, including themodern versions of cyanobacteria, supply the greater part of the planet’s breathable oxygen.

algae and other tiny organisms bubbling away in the sea blow out about 150 billion kilos ofthe stuff every year.

and they are amazingly prolific. the more frantic among them can yield a new generationin less than ten minutes; clostridium perfringens, the disagreeable little organism that causesgangrene, can reproduce in nine minutes. at such a rate, a single bacterium could theoreticallyproduce more offspring in two days than there are protons in the universe. “given an adequatesupply of nutrients, a single bacterial cell can generate 280,000 billion individuals in a singleday,” according to the belgian biochemist and nobel laureate christian de duve. in the sameperiod, a human cell can just about manage a single division.

about once every million divisions, they produce a mutant. usually this is bad luck for themutant—change is always risky for an organism—but just occasionally the new bacterium isendowed with some accidental advantage, such as the ability to elude or shrug off an attack ofantibiotics. with this ability to evolve rapidly goes another, even scarier advantage. bacteriashare information. any bacterium can take pieces of genetic coding from any other.

essentially, as margulis and sagan put it, all bacteria swim in a single gene pool. anyadaptive change that occurs in one area of the bacterial universe can spread to any other. it’srather as if a human could go to an insect to get the necessary genetic coding to sprout wingsor walk on ceilings. it means that from a genetic point of view bacteria have become a singlesuperorganism—tiny, dispersed, but invincible.

they will live and thrive on almost anything you spill, dribble, or shake loose. just givethem a little moisture—as when you run a damp cloth over a counter—and they will bloom asif created from nothing. they will eat wood, the glue in wallpaper, the metals in hardenedpaint. scientists in australia found microbes known as thiobacillus concretivorans that livedin—indeed, could not live without—concentrations of sulfuric acid strong enough to dissolvemetal. a species called micrococcus radiophilus was found living happily in the waste tanksof nuclear reactors, gorging itself on plutonium and whatever else was there. some bacteriabreak down chemical materials from which, as far as we can tell, they gain no benefit at all.

they have been found living in boiling mud pots and lakes of caustic soda, deep insiderocks, at the bottom of the sea, in hidden pools of icy water in the mcmurdo dry valleys ofantarctica, and seven miles down in the pacific ocean where pressures are more than athousand times greater than at the surface, or equivalent to being squashed beneath fiftyjumbo jets. some of them seem to be practically indestructible. deinococcus radiodurans is,according to theeconomist , “almost immune to radioactivity.” blast its dna with radiation,and the pieces immediately reform “like the scuttling limbs of an undead creature from ahorror movie.”

perhaps the most extraordinary survival yet found was that of a streptococcus bacteriumthat was recovered from the sealed lens of a camera that had stood on the moon for two years.

in short, there are few environments in which bacteria aren’t prepared to live. “they arefinding now that when they push probes into ocean vents so hot that the probes actually startto melt, there are bacteria even there,” victoria bennett told me.

in the 1920s two scientists at the university of chicago, edson bastin and frank greer,announced that they had isolated from oil wells strains of bacteria that had been living at
depths of two thousand feet. the notion was dismissed as fundamentally preposterous—therewas nothing to live on at two thousand feet—and for fifty years it was assumed that theirsamples had been contaminated with surface microbes. we now know that there are a lot ofmicrobes living deep within the earth, many of which have nothing at all to do with theorganic world. they eat rocks or, rather, the stuff that’s in rocks—iron, sulfur, manganese,and so on. and they breathe odd things too—iron, chromium, cobalt, even uranium. suchprocesses may be instrumental in concentrating gold, copper, and other precious metals, andpossibly deposits of oil and natural gas. it has even been suggested that their tireless nibblingscreated the earth’s crust.

some scientists now think that there could be as much as 100 trillion tons of bacteria livingbeneath our feet in what are known as subsurface lithoautotrophic microbial ecosystems—slime for short. thomas gold of cornell has estimated that if you took all the bacteria out ofthe earth’s interior and dumped it on the surface, it would cover the planet to a depth of fivefeet. if the estimates are correct, there could be more life under the earth than on top of it.

at depth microbes shrink in size and become extremely sluggish. the liveliest of them maydivide no more than once a century, some no more than perhaps once in five hundred years.

as the economist has put it: “the key to long life, it seems, is not to do too much.” whenthings are really tough, bacteria are prepared to shut down all systems and wait for bettertimes. in 1997 scientists successfully activated some anthrax spores that had lain dormant foreighty years in a museum display in trondheim, norway. other microorganisms have leaptback to life after being released from a 118-year-old can of meat and a 166-year-old bottle ofbeer. in 1996, scientists at the russian academy of science claimed to have revived bacteriafrozen in siberian permafrost for three million years. but the record claim for durability so faris one made by russell vreeland and colleagues at west chester university in pennsylvaniain 2000, when they announced that they had resuscitated 250-million-year-old bacteria calledbacillus permians that had been trapped in salt deposits two thousand feet underground incarlsbad, new mexico. if so, this microbe is older than the continents.

the report met with some understandable dubiousness. many biochemists maintained thatover such a span the microbe’s components would have become uselessly degraded unless thebacterium roused itself from time to time. however, if the bacterium did stir occasionallythere was no plausible internal source of energy that could have lasted so long. the moredoubtful scientists suggested that the sample may have been contaminated, if not during itsretrieval then perhaps while still buried. in 2001, a team from tel aviv university argued thatb. permians were almost identical to a strain of modern bacteria, bacillus marismortui, foundin the dead sea. only two of its genetic sequences differed, and then only slightly.

“are we to believe,” the israeli researchers wrote, “that in 250 million years b. permianshas accumulated the same amount of genetic differences that could be achieved in just 3–7days in the laboratory?” in reply, vreeland suggested that “bacteria evolve faster in the labthan they do in the wild.”

maybe.

it is a remarkable fact that well into the space age, most school textbooks divided the worldof the living into just two categories—plant and animal. microorganisms hardly featured.

amoebas and similar single-celled organisms were treated as proto-animals and algae as
proto-plants. bacteria were usually lumped in with plants, too, even though everyone knewthey didn’t belong there. as far back as the late nineteenth century the german naturalisternst haeckel had suggested that bacteria deserved to be placed in a separate kingdom, whichhe called monera, but the idea didn’t begin to catch on among biologists until the 1960s andthen only among some of them. (i note that my trusty american heritage desk dictionaryfrom 1969 doesn’t recognize the term.)many organisms in the visible world were also poorly served by the traditional division.

fungi, the group that includes mushrooms, molds, mildews, yeasts, and puffballs, were nearlyalways treated as botanical objects, though in fact almost nothing about them—how theyreproduce and respire, how they build themselves—matches anything in the plant world.

structurally they have more in common with animals in that they build their cells from chitin,a material that gives them their distinctive texture. the same substance is used to make theshells of insects and the claws of mammals, though it isn’t nearly so tasty in a stag beetle as ina portobello mushroom. above all, unlike all plants, fungi don’t photosynthesize, so theyhave no chlorophyll and thus are not green. instead they grow directly on their food source,which can be almost anything. fungi will eat the sulfur off a concrete wall or the decayingmatter between your toes—two things no plant will do. almost the only plantlike quality theyhave is that they root.

even less comfortably susceptible to categorization was the peculiar group of organismsformally called myxomycetes but more commonly known as slime molds. the name no doubthas much to do with their obscurity. an appellation that sounded a little more dynamic—“ambulant self-activating protoplasm,” say—and less like the stuff you find when you reachdeep into a clogged drain would almost certainly have earned these extraordinary entities amore immediate share of the attention they deserve, for slime molds are, make no mistake,among the most interesting organisms in nature. when times are good, they exist as one-celled individuals, much like amoebas. but when conditions grow tough, they crawl to acentral gathering place and become, almost miraculously, a slug. the slug is not a thing ofbeauty and it doesn’t go terribly far—usually just from the bottom of a pile of leaf litter to thetop, where it is in a slightly more exposed position—but for millions of years this may wellhave been the niftiest trick in the universe.

and it doesn’t stop there. having hauled itself up to a more favorable locale, the slimemold transforms itself yet again, taking on the form of a plant. by some curious orderlyprocess the cells reconfigure, like the members of a tiny marching band, to make a stalk atopof which forms a bulb known as a fruiting body. inside the fruiting body are millions ofspores that, at the appropriate moment, are released to the wind to blow away and becomesingle-celled organisms that can start the process again.

for years slime molds were claimed as protozoa by zoologists and as fungi by mycologists,though most people could see they didn’t really belong anywhere. when genetic testingarrived, people in lab coats were surprised to find that slime molds were so distinctive andpeculiar that they weren’t directly related to anything else in nature, and sometimes not evento each other.

in 1969, in an attempt to bring some order to the growing inadequacies of classification, anecologist from cornell university named r. h. whittaker unveiled in the journalscience aproposal to divide life into five principal branches—kingdoms, as they are known—calledanimalia, plantae, fungi, protista, and monera. protista, was a modification of an earlier
term, protoctista, which had been suggested a century earlier by a scottish biologist namedjohn hogg, and was meant to describe any organisms that were neither plant nor animal.

though whittaker’s new scheme was a great improvement, protista remained ill defined.

some taxonomists reserved it for large unicellular organisms—the eukaryotes—but otherstreated it as the kind of odd sock drawer of biology, putting into it anything that didn’t fitanywhere else. it included (depending on which text you consulted) slime molds, amoebas,and even seaweed, among much else. by one calculation it contained as many as 200,000different species of organism all told. that’s a lot of odd socks.

ironically, just as whittaker’s five-kingdom classification was beginning to find its wayinto textbooks, a retiring academic at the university of illinois was groping his way toward adiscovery that would challenge everything. his name was carl woese (rhymes with rose), andsince the mid-1960s—or about as early as it was possible to do so—he had been quietlystudying genetic sequences in bacteria. in the early days, this was an exceedingly painstakingprocess. work on a single bacterium could easily consume a year. at that time, according towoese, only about 500 species of bacteria were known, which is fewer than the number ofspecies you have in your mouth. today the number is about ten times that, though that is stillfar short of the 26,900 species of algae, 70,000 of fungi, and 30,800 of amoebas and relatedorganisms whose biographies fill the annals of biology.

it isn’t simple indifference that keeps the total low. bacteria can be exasperatingly difficultto isolate and study. only about 1 percent will grow in culture. considering how wildlyadaptable they are in nature, it is an odd fact that the one place they seem not to wish to live isa petri dish. plop them on a bed of agar and pamper them as you will, and most will just liethere, declining every inducement to bloom. any bacterium that thrives in a lab is bydefinition exceptional, and yet these were, almost exclusively, the organisms studied bymicrobiologists. it was, said woese, “like learning about animals from visiting zoos.”

genes, however, allowed woese to approach microorganisms from another angle. as heworked, woese realized that there were more fundamental divisions in the microbial worldthan anyone suspected. a lot of little organisms that looked like bacteria and behaved likebacteria were actually something else altogether—something that had branched off frombacteria a long time ago. woese called these organisms archaebacteria, later shortened toarchaea.

it has be said that the attributes that distinguish archaea from bacteria are not the sort thatwould quicken the pulse of any but a biologist. they are mostly differences in their lipids andan absence of something called peptidoglycan. but in practice they make a world ofdifference. archaeans are more different from bacteria than you and i are from a crab orspider. singlehandedly woese had discovered an unsuspected division of life, so fundamentalthat it stood above the level of kingdom at the apogee of the universal tree of life, as it israther reverentially known.

in 1976, he startled the world—or at least the little bit of it that was paying attention—byredrawing the tree of life to incorporate not five main divisions, but twenty-three. these hegrouped under three new principal categories—bacteria, archaea, and eukarya (sometimesspelled eucarya)—which he called domains.

woese’s new divisions did not take the biological world by storm. some dismissed them asmuch too heavily weighted toward the microbial. many just ignored them. woese, according
to frances ashcroft, “felt bitterly disappointed.” but slowly his new scheme began to catchon among microbiologists. botanists and zoologists were much slower to admire its virtues.

it’s not hard to see why. on woese’s model, the worlds of botany and zoology are relegatedto a few twigs on the outermost branch of the eukaryan limb. everything else belongs tounicellular beings.

“these folks were brought up to classify in terms of gross morphological similarities anddifferences,” woese told an interviewer in 1996. “the idea of doing so in terms of molecularsequence is a bit hard for many of them to swallow.” in short, if they couldn’t see a differencewith their own eyes, they didn’t like it. and so they persisted with the traditional five-kingdom division—an arrangement that woese called “not very useful” in his mildermoments and “positively misleading” much of the rest of the time. “biology, like physicsbefore it,” woese wrote, “has moved to a level where the objects of interest and theirinteractions often cannot be perceived through direct observation.”

in 1998 the great and ancient harvard zoologist ernst mayr (who then was in his ninety-fourth year and at the time of my writing is nearing one hundred and still going strong) stirredthe pot further by declaring that there should be just two prime divisions of life—“empires”

he called them. in a paper published in the proceedings of the national academy of sciences,mayr said that woese’s findings were interesting but ultimately misguided, noting that“woese was not trained as a biologist and quite naturally does not have an extensivefamiliarity with the principles of classification,” which is perhaps as close as onedistinguished scientist can come to saying of another that he doesn’t know what he is talkingabout.

the specifics of mayr’s criticisms are too technical to need extensive airing here—theyinvolve issues of meiotic sexuality, hennigian cladification, and controversial interpretationsof the genome of methanobacterium thermoautrophicum, among rather a lot else—butessentially he argues that woese’s arrangement unbalances the tree of life. the bacterialrealm, mayr notes, consists of no more than a few thousand species while the archaean has amere 175 named specimens, with perhaps a few thousand more to be found—“but hardlymore than that.” by contrast, the eukaryotic realm—that is, the complicated organisms withnucleated cells, like us—numbers already in the millions. for the sake of “the principle ofbalance,” mayr argues for combining the simple bacterial organisms in a single category,prokaryota, while placing the more complex and “highly evolved” remainder in the empireeukaryota, which would stand alongside as an equal. put another way, he argues for keepingthings much as they were before. this division between simple cells and complex cells “iswhere the great break is in the living world.”

the distinction between halophilic archaeans and methanosarcina or between flavobacteriaand gram-positive bacteria clearly will never be a matter of moment for most of us, but it isworth remembering that each is as different from its neighbors as animals are from plants. ifwoese’s new arrangement teaches us anything it is that life really is various and that most ofthat variety is small, unicellular, and unfamiliar. it is a natural human impulse to think ofevolution as a long chain of improvements, of a never-ending advance toward largeness andcomplexity—in a word, toward us. we flatter ourselves. most of the real diversity inevolution has been small-scale. we large things are just flukes—an interesting side branch. ofthe twenty-three main divisions of life, only three—plants, animals, and fungi—are largeenough to be seen by the human eye, and even they contain species that are microscopic.

indeed, according to woese, if you totaled up all the biomass of the planet—every living
thing, plants included—microbes would account for at least 80 percent of all there is, perhapsmore. the world belongs to the very small—and it has for a very long time.

so why, you are bound to ask at some point in your life, do microbes so often want to hurtus? what possible satisfaction could there be to a microbe in having us grow feverish orchilled, or disfigured with sores, or above all expire? a dead host, after all, is hardly going toprovide long-term hospitality.

to begin with, it is worth remembering that most microorganisms are neutral or evenbeneficial to human well-being. the most rampantly infectious organism on earth, abacterium called wolbachia, doesn’t hurt humans at all—or, come to that, any othervertebrates—but if you are a shrimp or worm or fruit fly, it can make you wish you had neverbeen born. altogether, only about one microbe in a thousand is a pathogen for humans,according to national geographic —though, knowing what some of them can do, we couldbe forgiven for thinking that that is quite enough. even if mostly benign, microbes are still thenumber-three killer in the western world, and even many less lethal ones of course make usdeeply rue their existence.

making a host unwell has certain benefits for the microbe. the symptoms of an illnessoften help to spread the disease. vomiting, sneezing, and diarrhea are excellent methods ofgetting out of one host and into position for another. the most effective strategy of all is toenlist the help of a mobile third party. infectious organisms love mosquitoes because themosquito’s sting delivers them directly to a bloodstream where they can get straight to workbefore the victim’s defense mechanisms can figure out what’s hit them. this is why so manygrade-a diseases—malaria, yellow fever, dengue fever, encephalitis, and a hundred or soother less celebrated but often rapacious maladies—begin with a mosquito bite. it is afortunate fluke for us that hiv, the aids agent, isn’t among them—at least not yet. any hivthe mosquito sucks up on its travels is dissolved by the mosquito’s own metabolism. whenthe day comes that the virus mutates its way around this, we may be in real trouble.

it is a mistake, however, to consider the matter too carefully from the position of logicbecause microorganisms clearly are not calculating entities. they don’t care what they do toyou any more than you care what distress you cause when you slaughter them by the millionswith a soapy shower or a swipe of deodorant. the only time your continuing well-being is ofconsequence to a pathogen is when it kills you too well. if they eliminate you before they canmove on, then they may well die out themselves. this in fact sometimes happens. history,jared diamond notes, is full of diseases that “once caused terrifying epidemics and thendisappeared as mysteriously as they had come.” he cites the robust but mercifully transientenglish sweating sickness, which raged from 1485 to 1552, killing tens of thousands as itwent, before burning itself out. too much efficiency is not a good thing for any infectiousorganism.

a great deal of sickness arises not because of what the organism has done to you but whatyour body is trying to do to the organism. in its quest to rid the body of pathogens, theimmune system sometimes destroys cells or damages critical tissues, so often when you areunwell what you are feeling is not the pathogens but your own immune responses. anyway,getting sick is a sensible response to infection. sick people retire to their beds and thus areless of a threat to the wider community. resting also frees more of the body’s resources toattend to the infection.

because there are so many things out there with the potential to hurt you, your body holdslots of different varieties of defensive white cells—some ten million types in all, eachdesigned to identify and destroy a particular sort of invader. it would be impossibly inefficientto maintain ten million separate standing armies, so each variety of white cell keeps only afew scouts on active duty. when an infectious agent—what’s known as an antigen—invades,relevant scouts identify the attacker and put out a call for reinforcements of the right type.

while your body is manufacturing these forces, you are likely to feel wretched. the onset ofrecovery begins when the troops finally swing into action.

white cells are merciless and will hunt down and kill every last pathogen they can find. toavoid extinction, attackers have evolved two elemental strategies. either they strike quicklyand move on to a new host, as with common infectious illnesses like flu, or they disguisethemselves so that the white cells fail to spot them, as with hiv, the virus responsible foraids, which can sit harmlessly and unnoticed in the nuclei of cells for years before springinginto action.

one of the odder aspects of infection is that microbes that normally do no harm at allsometimes get into the wrong parts of the body and “go kind of crazy,” in the words of dr.

bryan marsh, an infectious diseases specialist at dartmouth–hitchcock medical center inlebanon, new hamphire. “it happens all the time with car accidents when people sufferinternal injuries. microbes that are normally benign in the gut get into other parts of thebody—the bloodstream, for instance—and cause terrible havoc.”

the scariest, most out-of-control bacterial disorder of the moment is a disease callednecrotizing fasciitis in which bacteria essentially eat the victim from the inside out, devouringinternal tissue and leaving behind a pulpy, noxious residue. patients often come in withcomparatively mild complaints—a skin rash and fever typically—but then dramaticallydeteriorate. when they are opened up it is often found that they are simply being consumed.

the only treatment is what is known as “radical excisional surgery”—cutting out every bit ofinfected area. seventy percent of victims die; many of the rest are left terribly disfigured. thesource of the infection is a mundane family of bacteria called group a streptococcus, whichnormally do no more than cause strep throat. very occasionally, for reasons unknown, someof these bacteria get through the lining of the throat and into the body proper, where theywreak the most devastating havoc. they are completely resistant to antibiotics. about athousand cases a year occur in the united states, and no one can say that it won’t get worse.

precisely the same thing happens with meningitis. at least 10 percent of young adults, andperhaps 30 percent of teenagers, carry the deadly meningococcal bacterium, but it lives quiteharmlessly in the throat. just occasionally—in about one young person in a hundredthousand—it gets into the bloodstream and makes them very ill indeed. in the worst cases,death can come in twelve hours. that’s shockingly quick. “you can have a person who’s inperfect health at breakfast and dead by evening,” says marsh.

we would have much more success with bacteria if we weren’t so profligate with our bestweapon against them: antibiotics. remarkably, by one estimate some 70 percent of theantibiotics used in the developed world are given to farm animals, often routinely in stockfeed, simply to promote growth or as a precaution against infection. such applications givebacteria every opportunity to evolve a resistance to them. it is an opportunity that they haveenthusiastically seized.

in 1952, penicillin was fully effective against all strains of staphylococcus bacteria, to suchan extent that by the early 1960s the u.s. surgeon general, william stewart, felt confidentenough to declare: “the time has come to close the book on infectious diseases. we havebasically wiped out infection in the united states.” even as he spoke, however, some 90percent of those strains were in the process of developing immunity to penicillin. soon one ofthese new strains, called methicillin-resistant staphylococcus aureus, began to show up inhospitals. only one type of antibiotic, vancomycin, remained effective against it, but in 1997a hospital in tokyo reported the appearance of a strain that could resist even that. withinmonths it had spread to six other japanese hospitals. all over, the microbes are beginning towin the war again: in u.s. hospitals alone, some fourteen thousand people a year die frominfections they pick up there. as james surowiecki has noted, given a choice betweendeveloping antibiotics that people will take every day for two weeks or antidepressants thatpeople will take every day forever, drug companies not surprisingly opt for the latter.

although a few antibiotics have been toughened up a bit, the pharmaceutical industry hasn’tgiven us an entirely new antibiotic since the 1970s.

our carelessness is all the more alarming since the discovery that many other ailments maybe bacterial in origin. the process of discovery began in 1983 when barry marshall, a doctorin perth, western australia, found that many stomach cancers and most stomach ulcers arecaused by a bacterium called helicobacter pylori. even though his findings were easily tested,the notion was so radical that more than a decade would pass before they were generallyaccepted. america’s national institutes of health, for instance, didn’t officially endorse theidea until 1994. “hundreds, even thousands of people must have died from ulcers whowouldn’t have,” marshall told a reporter from forbes in 1999.

since then further research has shown that there is or may well be a bacterial component inall kinds of other disorders—heart disease, asthma, arthritis, multiple sclerosis, several typesof mental disorders, many cancers, even, it has been suggested (inscience no less), obesity.

the day may not be far off when we desperately require an effective antibiotic and haven’tgot one to call on.

it may come as a slight comfort to know that bacteria can themselves get sick. they aresometimes infected by bacteriophages (or simply phages), a type of virus. a virus is a strangeand unlovely entity—“a piece of nucleic acid surrounded by bad news” in the memorablephrase of the nobel laureate peter medawar. smaller and simpler than bacteria, viruses aren’tthemselves alive. in isolation they are inert and harmless. but introduce them into a suitablehost and they burst into busyness—into life. about five thousand types of virus are known,and between them they afflict us with many hundreds of diseases, ranging from the flu andcommon cold to those that are most invidious to human well-being: smallpox, rabies, yellowfever, ebola, polio, and the human immunodeficiency virus, the source of aids.

viruses prosper by hijacking the genetic material of a living cell and using it to producemore virus. they reproduce in a fanatical manner, then burst out in search of more cells toinvade. not being living organisms themselves, they can afford to be very simple. many,including hiv, have ten genes or fewer, whereas even the simplest bacteria require severalthousand. they are also very tiny, much too small to be seen with a conventional microscope.

it wasn’t until 1943 and the invention of the electron microscope that science got its first lookat them. but they can do immense damage. smallpox in the twentieth century alone killed anestimated 300 million people.

they also have an unnerving capacity to burst upon the world in some new and startlingform and then to vanish again as quickly as they came. in 1916, in one such case, people ineurope and america began to come down with a strange sleeping sickness, which becameknown as encephalitis lethargica. victims would go to sleep and not wake up. they could beroused without great difficulty to take food or go to the lavatory, and would answer questionssensibly—they knew who and where they were—though their manner was always apathetic.

however, the moment they were permitted to rest, they would sink at once back intodeepest slumber and remain in that state for as long as they were left. some went on in thismanner for months before dying. a very few survived and regained consciousness but nottheir former liveliness. they existed in a state of profound apathy, “like extinct volcanoes,” inthe words of one doctor. in ten years the disease killed some five million people and thenquietly went away. it didn’t get much lasting attention because in the meantime an even worseepidemic—indeed, the worst in history—swept across the world.

it is sometimes called the great swine flu epidemic and sometimes the great spanish fluepidemic, but in either case it was ferocious. world war i killed twenty-one million people infour years; swine flu did the same in its first four months. almost 80 percent of americancasualties in the first world war came not from enemy fire, but from flu. in some units themortality rate was as high as 80 percent.

swine flu arose as a normal, nonlethal flu in the spring of 1918, but somehow over thefollowing months—no one knows how or where—it mutated into something more severe. afifth of victims suffered only mild symptoms, but the rest became gravely ill and often died.

some succumbed within hours; others held on for a few days.

in the united states, the first deaths were recorded among sailors in boston in late august1918, but the epidemic quickly spread to all parts of the country. schools closed, publicentertainments were shut down, people everywhere wore masks. it did little good. betweenthe autumn of 1918 and spring of the following year, 548,452 people died of the flu inamerica. the toll in britain was 220,000, with similar numbers dead in france and germany.

no one knows the global toll, as records in the third world were often poor, but it was notless than 20 million and probably more like 50 million. some estimates have put the globaltotal as high as 100 million.

in an attempt to devise a vaccine, medical authorities conducted tests on volunteers at amilitary prison on deer island in boston harbor. the prisoners were promised pardons if theysurvived a battery of tests. these tests were rigorous to say the least. first the subjects wereinjected with infected lung tissue taken from the dead and then sprayed in the eyes, nose, andmouth with infectious aerosols. if they still failed to succumb, they had their throats swabbedwith discharges taken from the sick and dying. if all else failed, they were required to sitopen-mouthed while a gravely ill victim was helped to cough into their faces.

out of—somewhat amazingly—three hundred men who volunteered, the doctors chosesixty-two for the tests. none contracted the flu—not one. the only person who did grow illwas the ward doctor, who swiftly died. the probable explanation for this is that the epidemichad passed through the prison a few weeks earlier and the volunteers, all of whom hadsurvived that visitation, had a natural immunity.

much about the 1918 flu is understood poorly or not at all. one mystery is how it eruptedsuddenly, all over, in places separated by oceans, mountain ranges, and other earthly
impediments. a virus can survive for no more than a few hours outside a host body, so howcould it appear in madrid, bombay, and philadelphia all in the same week?

the probable answer is that it was incubated and spread by people who had only slightsymptoms or none at all. even in normal outbreaks, about 10 percent of people have the flubut are unaware of it because they experience no ill effects. and because they remain incirculation they tend to be the great spreaders of the disease.

that would account for the 1918 outbreak’s widespread distribution, but it still doesn’texplain how it managed to lay low for several months before erupting so explosively at moreor less the same time all over. even more mysterious is that it was primarily devastating topeople in the prime of life. flu normally is hardest on infants and the elderly, but in the 1918outbreak deaths were overwhelmingly among people in their twenties and thirties. olderpeople may have benefited from resistance gained from an earlier exposure to the same strain,but why the very young were similarly spared is unknown. the greatest mystery of all is whythe 1918 flu was so ferociously deadly when most flus are not. we still have no idea.

from time to time certain strains of virus return. a disagreeable russian virus known ash1n1 caused severe outbreaks over wide areas in 1933, then again in the 1950s, and yet againin the 1970s. where it went in the meantime each time is uncertain. one suggestion is thatviruses hide out unnoticed in populations of wild animals before trying their hand at a newgeneration of humans. no one can rule out the possibility that the great swine flu epidemicmight once again rear its head.

and if it doesn’t, others well might. new and frightening viruses crop up all the time.

ebola, lassa, and marburg fevers all have tended to flare up and die down again, but no onecan say that they aren’t quietly mutating away somewhere, or simply awaiting the rightopportunity to burst forth in a catastrophic manner. it is now apparent that aids has beenamong us much longer than anyone originally suspected. researchers at the manchesterroyal infirmary in england discovered that a sailor who had died of mysterious, untreatablecauses in 1959 in fact had aids. but for whatever reasons the disease remained generallyquiescent for another twenty years.

the miracle is that other such diseases haven’t gone rampant. lassa fever, which wasn’tfirst detected until 1969, in west africa, is extremely virulent and little understood. in 1969, adoctor at a yale university lab in new haven, connecticut, who was studying lassa fevercame down with it. he survived, but, more alarmingly, a technician in a nearby lab, with nodirect exposure, also contracted the disease and died.

happily the outbreak stopped there, but we can’t count on such good fortune always. ourlifestyles invite epidemics. air travel makes it possible to spread infectious agents across theplanet with amazing ease. an ebola virus could begin the day in, say, benin, and finish it innew york or hamburg or nairobi, or all three. it means also that medical authoritiesincreasingly need to be acquainted with pretty much every malady that exists everywhere, butof course they are not. in 1990, a nigerian living in chicago was exposed to lassa fever on avisit to his homeland, but didn’t develop symptoms until he had returned to the united states.

he died in a chicago hospital without diagnosis and without anyone taking any specialprecautions in treating him, unaware that he had one of the most lethal and infectious diseaseson the planet. miraculously, no one else was infected. we may not be so lucky next time.

and on that sobering note, it’s time to return to the world of the visibly living.

21    LIFE GOES ON

it isn’t easy to become a fossil. the fate of nearly all living organisms—over 99.9percent of them—is to compost down to nothingness. when your spark is gone, everymolecule you own will be nibbled off you or sluiced away to be put to use in some othersystem. that’s just the way it is. even if you make it into the small pool of organisms, the lessthan 0.1 percent, that don’t get devoured, the chances of being fossilized are very small.

in order to become a fossil, several things must happen. first, you must die in the rightplace. only about 15 percent of rocks can preserve fossils, so it’s no good keeling over on afuture site of granite. in practical terms the deceased must become buried in sediment, whereit can leave an impression, like a leaf in wet mud, or decompose without exposure to oxygen,permitting the molecules in its bones and hard parts (and very occasionally softer parts) to bereplaced by dissolved minerals, creating a petrified copy of the original. then as thesediments in which the fossil lies are carelessly pressed and folded and pushed about byearth’s processes, the fossil must somehow maintain an identifiable shape. finally, but aboveall, after tens of millions or perhaps hundreds of millions of years hidden away, it must befound and recognized as something worth keeping.

only about one bone in a billion, it is thought, ever becomes fossilized. if that is so, itmeans that the complete fossil legacy of all the americans alive today—that’s 270 millionpeople with 206 bones each—will only be about fifty bones, one quarter of a completeskeleton. that’s not to say of course that any of these bones will actually be found. bearing inmind that they can be buried anywhere within an area of slightly over 3.6 million squaremiles, little of which will ever be turned over, much less examined, it would be something ofa miracle if they were. fossils are in every sense vanishingly rare. most of what has lived onearth has left behind no record at all. it has been estimated that less than one species in tenthousand has made it into the fossil record. that in itself is a stunningly infinitesimalproportion. however, if you accept the common estimate that the earth has produced 30billion species of creature in its time and richard leakey and roger lewin’s statement (inthe sixth extinction ) that there are 250,000 species of creature in the fossil record, thatreduces the proportion to just one in 120,000. either way, what we possess is the merestsampling of all the life that earth has spawned.

moreover, the record we do have is hopelessly skewed. most land animals, of course, don’tdie in sediments. they drop in the open and are eaten or left to rot or weather down tonothing. the fossil record consequently is almost absurdly biased in favor of marine creatures.

about 95 percent of all the fossils we possess are of animals that once lived under water,mostly in shallow seas.

i mention all this to explain why on a gray day in february i went to the natural historymuseum in london to meet a cheerful, vaguely rumpled, very likeable paleontologist namedrichard fortey.

fortey knows an awful lot about an awful lot. he is the author of a wry, splendid bookcalled life: an unauthorised biography, which covers the whole pageant of animate creation.

but his first love is a type of marine creature called trilobites that once teemed in ordovicianseas but haven’t existed for a long time except in fossilized form. all shared a basic body planof three parts, or lobes—head, tail, thorax—from which comes the name. fortey found hisfirst when he was a boy clambering over rocks at st. david’s bay in wales. he was hookedfor life.

he took me to a gallery of tall metal cupboards. each cupboard was filled with shallowdrawers, and each drawer was filled with stony trilobites—twenty thousand specimens in all.

“it seems like a big number,” he agreed, “but you have to remember that millions uponmillions of trilobites lived for millions upon millions of years in ancient seas, so twentythousand isn’t a huge number. and most of these are only partial specimens. finding acomplete trilobite fossil is still a big moment for a paleontologist.”

trilobites first appeared—fully formed, seemingly from nowhere—about 540 million yearsago, near the start of the great outburst of complex life popularly known as the cambrianexplosion, and then vanished, along with a great deal else, in the great and still mysteriouspermian extinction 300,000 or so centuries later. as with all extinct creatures, there is anatural temptation to regard them as failures, but in fact they were among the most successfulanimals ever to live. their reign ran for 300 million years—twice the span of dinosaurs,which were themselves one of history’s great survivors. humans, fortey points out, havesurvived so far for one-half of 1 percent as long.

with so much time at their disposal, the trilobites proliferated prodigiously. most remainedsmall, about the size of modern beetles, but some grew to be as big as platters. altogetherthey formed at least five thousand genera and sixty thousand species—though more turn upall the time. fortey had recently been at a conference in south america where he wasapproached by an academic from a small provincial university in argentina. “she had a boxthat was full of interesting things—trilobites that had never been seen before in southamerica, or indeed anywhere, and a great deal else. she had no research facilities to studythem and no funds to look for more. huge parts of the world are still unexplored.”

“in terms of trilobites?”

“no, in terms of everything.”

throughout the nineteenth century, trilobites were almost the only known forms of earlycomplex life, and for that reason were assiduously collected and studied. the big mysteryabout them was their sudden appearance. even now, as fortey says, it can be startling to go tothe right formation of rocks and to work your way upward through the eons finding no visiblelife at all, and then suddenly “a whole profallotaspis or elenellus as big as a crab will popinto your waiting hands.” these were creatures with limbs, gills, nervous systems, probingantennae, “a brain of sorts,” in fortey’s words, and the strangest eyes ever seen. made of
calcite rods, the same stuff that forms limestone, they constituted the earliest visual systemsknown. more than this, the earliest trilobites didn’t consist of just one venturesome speciesbut dozens, and didn’t appear in one or two locations but all over. many thinking people inthe nineteenth century saw this as proof of god’s handiwork and refutation of darwin’sevolutionary ideals. if evolution proceeded slowly, they asked, then how did he account forthis sudden appearance of complex, fully formed creatures? the fact is, he couldn’t.

and so matters seemed destined to remain forever until one day in 1909, three months shyof the fiftieth anniversary of the publication of darwin’s on the origin of species , when apaleontologist named charles doolittle walcott made an extraordinary find in the canadianrockies.

walcott was born in 1850 and grew up near utica, new york, in a family of modest means,which became more modest still with the sudden death of his father when walcott was aninfant. as a boy walcott discovered that he had a knack for finding fossils, particularlytrilobites, and built up a collection of sufficient distinction that it was bought by louisagassiz for his museum at harvard for a small fortune—about $70,000 in today’s money.

although he had barely a high school education and was self taught in the sciences, walcottbecame a leading authority on trilobites and was the first person to establish that trilobiteswere arthropods, the group that includes modern insects and crustaceans.

in 1879 he took a job as a field researcher with the newly formed united states geologicalsurvey and served with such distinction that within fifteen years he had risen to be its head. in1907 he was appointed secretary of the smithsonian institution, where he remained until hisdeath in 1927. despite his administrative obligations, he continued to do fieldwork and towrite prolifically. “his books fill a library shelf,” according to fortey. not incidentally, hewas also a founding director of the national advisory committee for aeronautics, whicheventually became the national aeronautics and space agency, or nasa, and thus canrightly be considered the grandfather of the space age.

but what he is remembered for now is an astute but lucky find in british columbia, highabove the little town of field, in the late summer of 1909. the customary version of the storyis that walcott, accompanied by his wife, was riding on horseback on a mountain trail beneaththe spot called the burgess ridge when his wife’s horse slipped on loose stones. dismountingto assist her, walcott discovered that the horse had turned a slab of shale that contained fossilcrustaceans of an especially ancient and unusual type. snow was falling—winter comes earlyto the canadian rockies—so they didn’t linger, but the next year at the first opportunitywalcott returned to the spot. tracing the presumed route of the rocks’ slide, he climbed 750feet to near the mountain’s summit. there, 8,000 feet above sea level, he found a shaleoutcrop, about the length of a city block, containing an unrivaled array of fossils from soonafter the moment when complex life burst forth in dazzling profusion—the famous cambrianexplosion. walcott had found, in effect, the holy grail of paleontology. the outcrop becameknown as the burgess shale, and for a long time it provided “our sole vista upon the inceptionof modern life in all its fullness,” as the late stephen jay gould recorded in his popular bookwonderful life .

gould, ever scrupulous, discovered from reading walcott’s diaries that the story of theburgess shale’s discovery appears to have been somewhat embroidered—walcott makes nomention of a slipping horse or falling snow—but there is no disputing that it was anextraordinary find.

it is almost impossible for us whose time on earth is limited to a breezy few decades toappreciate how remote in time from us the cambrian outburst was. if you could fly backwardsinto the past at the rate of one year per second, it would take you about half an hour to reachthe time of christ, and a little over three weeks to get back to the beginnings of human life.

but it would take you twenty years to reach the dawn of the cambrian period. it was, in otherwords, an extremely long time ago, and the world was a very different place.

for one thing, 500-million-plus years ago when the burgess shale was formed it wasn’t atthe top of a mountain but at the foot of one. specifically it was a shallow ocean basin at thebottom of a steep cliff. the seas of that time teemed with life, but normally the animals left norecord because they were soft-bodied and decayed upon dying. but at burgess the cliffcollapsed, and the creatures below, entombed in a mudslide, were pressed like flowers in abook, their features preserved in wondrous detail.

in annual summer trips from 1910 to 1925 (by which time he was seventy-five years old),walcott excavated tens of thousands of specimens (gould says 80,000; the normallyunimpeachable fact checkers of national georgraphic say 60,000), which he brought back towashington for further study. in both sheer numbers and diversity the collection wasunparalleled. some of the burgess fossils had shells; many others did not. some were sighted,others blind. the variety was enormous, consisting of 140 species by one count. “the burgessshale included a range of disparity in anatomical designs never again equaled, and notmatched today by all the creatures in the world’s oceans,” gould wrote.

unfortunately, according to gould, walcott failed to discern the significance of what hehad found. “snatching defeat from the jaws of victory,” gould wrote in another work, eightlittle piggies, “walcott then proceeded to misinterpret these magnificent fossils in the deepestpossible way.” he placed them into modern groups, making them ancestral to today’s worms,jellyfish, and other creatures, and thus failed to appreciate their distinctness. “under such aninterpretation,” gould sighed, “life began in primordial simplicity and moved inexorably,predictably onward to more and better.”

walcott died in 1927 and the burgess fossils were largely forgotten. for nearly half acentury they stayed shut away in drawers in the american museum of natural history inwashington, seldom consulted and never questioned. then in 1973 a graduate student fromcambridge university named simon conway morris paid a visit to the collection. he wasastonished by what he found. the fossils were far more varied and magnificent than walcotthad indicated in his writings. in taxonomy the category that describes the basic body plans ofall organisms is the phylum, and here, conway morris concluded, were drawer after drawer ofsuch anatomical singularities—all amazingly and unaccountably unrecognized by the manwho had found them.

with his supervisor, harry whittington, and fellow graduate student derek briggs, conwaymorris spent the next several years making a systematic revision of the entire collection, andcranking out one exciting monograph after another as discovery piled upon discovery. manyof the creatures employed body plans that were not simply unlike anything seen before orsince, but were bizarrely different. one, opabinia, had five eyes and a nozzle-like snout withclaws on the end. another, a disc-shaped being called peytoia, looked almost comically like apineapple slice. a third had evidently tottered about on rows of stilt-like legs, and was so oddthat they named it hallucigenia. there was so much unrecognized novelty in the collectionthat at one point upon opening a new drawer conway morris famously was heard to mutter,“oh fuck, not another phylum.”

the english team’s revisions showed that the cambrian had been a time of unparalleledinnovation and experimentation in body designs. for almost four billion years life haddawdled along without any detectable ambitions in the direction of complexity, and thensuddenly, in the space of just five or ten million years, it had created all the basic bodydesigns still in use today. name a creature, from a nematode worm to cameron diaz, and theyall use architecture first created in the cambrian party.

what was most surprising, however, was that there were so many body designs that hadfailed to make the cut, so to speak, and left no descendants. altogether, according to gould, atleast fifteen and perhaps as many as twenty of the burgess animals belonged to no recognizedphylum. (the number soon grew in some popular accounts to as many as one hundred—farmore than the cambridge scientists ever actually claimed.) “the history of life,” wrote gould,“is a story of massive removal followed by differentiation within a few surviving stocks, notthe conventional tale of steadily increasing excellence, complexity, and diversity.”

evolutionary success, it appeared, was a lottery.

one creature thatdid manage to slip through, a small wormlike being called pikaiagracilens, was found to have a primitive spinal column, making it the earliest known ancestorof all later vertebrates, including us.pikaia were by no means abundant among the burgessfossils, so goodness knows how close they may have come to extinction. gould, in a famousquotation, leaves no doubt that he sees our lineal success as a fortunate fluke: “wind back thetape of life to the early days of the burgess shale; let it play again from an identical startingpoint, and the chance becomes vanishingly small that anything like human intelligence wouldgrace the replay.”

gould’s book was published in 1989 to general critical acclaim and was a great commercialsuccess. what wasn’t generally known was that many scientists didn’t agree with gould’sconclusions at all, and that it was all soon to get very ugly. in the context of the cambrian,“explosion” would soon have more to do with modern tempers than ancient physiologicalfacts.

in fact, we now know, complex organisms existed at least a hundred million years beforethe cambrian. we should have known a whole lot sooner. nearly forty years after walcottmade his discovery in canada, on the other side of the planet in australia, a young geologistnamed reginald sprigg found something even older and in its way just as remarkable.

in 1946 sprigg was a young assistant government geologist for the state of south australiawhen he was sent to make a survey of abandoned mines in the ediacaran hills of the flindersrange, an expanse of baking outback some three hundred miles north of adelaide. the ideawas to see if there were any old mines that might be profitably reworked using newertechnologies, so he wasn’t studying surface rocks at all, still less fossils. but one day whileeating his lunch, sprigg idly overturned a hunk of sandstone and was surprised—to put itmildly—to see that the rock’s surface was covered in delicate fossils, rather like theimpressions leaves make in mud. these rocks predated the cambrian explosion. he waslooking at the dawn of visible life.

sprigg submitted a paper to nature , but it was turned down. he read it instead at the nextannual meeting of the australian and new zealand association for the advancement ofscience, but it failed to find favor with the association’s head, who said the ediacaran
imprints were merely “fortuitous inorganic markings”—patterns made by wind or rain ortides, but not living beings. his hopes not yet entirely crushed, sprigg traveled to london andpresented his findings to the 1948 international geological congress, but failed to exciteeither interest or belief. finally, for want of a better outlet, he published his findings in thetransactions of the royal society of south australia. then he quit his government job andtook up oil exploration.

nine  years  later,  in  1957,  a  schoolboy  named john mason, while walking throughcharnwood forest in the english midlands, found a rock with a strange fossil in it, similar toa modern sea pen and exactly like some of the specimens sprigg had found and been trying totell everyone about ever since. the schoolboy turned it in to a paleontologist at the universityof leicester, who identified it at once as precambrian. young mason got his picture in thepapers and was treated as a precocious hero; he still is in many books. the specimen wasnamed in his honor chamia masoni.

today some of sprigg’s original ediacaran specimens, along with many of the other fifteenhundred specimens that have been found throughout the flinders range since that time, canbe seen in a glass case in an upstairs room of the stout and lovely south australian museumin adelaide, but they don’t attract a great deal of attention. the delicately etched patterns arerather faint and not terribly arresting to the untrained eye. they are mostly small and disc-shaped, with occasional, vague trailing ribbons. fortey has described them as “soft-bodiedoddities.”

there is still very little agreement about what these things were or how they lived. theyhad, as far as can be told, no mouth or anus with which to take in and discharge digestivematerials, and no internal organs with which to process them along the way. “in life,” forteysays, “most of them probably simply lay upon the surface of the sandy sediment, like soft,structureless and inanimate flatfish.” at their liveliest, they were no more complex thanjellyfish. all the ediacaran creatures were diploblastic, meaning they were built from twolayers of tissue. with the exception of jellyfish, all animals today are triploblastic.

some experts think they weren’t animals at all, but more like plants or fungi. thedistinctions between plant and animal are not always clear even now. the modern spongespends its life fixed to a single spot and has no eyes or brain or beating heart, and yet is ananimal. “when we go back to the precambrian the differences between plants and animalswere probably even less clear,” says fortey. “there isn’t any rule that says you have to bedemonstrably one or the other.”

nor is it agreed that the ediacaran organisms are in any way ancestral to anything alivetoday (except possibly some jellyfish). many authorities see them as a kind of failedexperiment, a stab at complexity that didn’t take, possibly because the sluggish ediacaranorganisms were devoured or outcompeted by the lither and more sophisticated animals of thecambrian period.

“there is nothing closely similar alive today,” fortey has written. “they are difficult tointerpret as any kind of ancestors of what was to follow.”

the feeling was that ultimately they weren’t terribly important to the development of lifeon earth. many authorities believe that there was a mass extermination at the precambrian–cambrian boundary and that all the ediacaran creatures (except the uncertain jellyfish) failed
to move on to the next phase. the real business of complex life, in other words, started withthe cambrian explosion. that’s how gould saw it in any case.

as for the revisions of the burgess shale fossils, almost at once people began to questionthe interpretations and, in particular, gould’s interpretation of the interpretations. “from thefirst there were a number of scientists who doubted the account that steve gould hadpresented, however much they admired the manner of its delivery,” fortey wrote in life. thatis putting it mildly.

“if only stephen gould could think as clearly as he writes!” barked the oxford academicrichard dawkins in the opening line of a review (in the london sunday telegraph) ofwonderful life. dawkins acknowledged that the book was “unputdownable” and a “literarytour-de-force,” but accused gould of engaging in a “grandiloquent and near-disingenuous”

misrepresentation of the facts by suggesting that the burgess revisions had stunned thepaleontological community. “the view that he is attacking—that evolution marchesinexorably toward a pinnacle such as man—has not been believed for 50 years,” dawkinsfumed.

and yet that was exactly the conclusion to which many general reviewers were drawn.

one, writing in the new york times book review, cheerfully suggested that as a result ofgould’s book scientists “have been throwing out some preconceptions that they had notexamined for generations. they are, reluctantly or enthusiastically, accepting the idea thathumans are as much an accident of nature as a product of orderly development.”

but the real heat directed at gould arose from the belief that many of his conclusions weresimply mistaken or carelessly inflated. writing in the journal evolution, dawkins attackedgould’s assertions that “evolution in the cambrian was a different kind of process fromtoday” and expressed exasperation at gould’s repeated suggestions that “the cambrian was aperiod of evolutionary ‘experiment,’ evolutionary ‘trial and error,’ evolutionary ‘false starts.’ .

. . it was the fertile time when all the great ‘fundamental body plans’ were invented.

nowadays, evolution just tinkers with old body plans. back in the cambrian, new phyla andnew classes arose. nowadays we only get new species!”

noting how often this idea—that there are no new body plans—is picked up, dawkins says:

“it is as though a gardener looked at an oak tree and remarked, wonderingly: ‘isn’t it strangethat no major new boughs have appeared on this tree for many years? these days, all the newgrowth appears to be at the twig level.’ ”

“it was a strange time,” fortey says now, “especially when you reflected that this was allabout something that happened five hundred million years ago, but feelings really did runquite high. i joked in one of my books that i felt as if i ought to put a safety helmet on beforewriting about the cambrian period, but it did actually feel a bit like that.”

strangest of all was the response of one of the heroes of wonderful life, simon conwaymorris, who startled many in the paleontological community by rounding abruptly on gouldin a book of his own, the crucible of creation. the book treated gould “with contempt, evenloathing,” in fortey’s words. “i have never encountered such spleen in a book by aprofessional,” fortey wrote later. “the casual reader of the crucible of creation, unaware of
the history, would never gather that the author’s views had once been close to (if not actuallyshared with) gould’s.”

when i asked fortey about it, he said: “well, it was very strange, quite shocking really,because gould’s portrayal of him had been so flattering. i could only assume that simon wasembarrassed. you know, science changes but books are permanent, and i suppose he regrettedbeing so irremediably associated with views that he no longer altogether held. there was allthat stuff about ‘oh fuck, another phylum’ and i expect he regretted being famous for that.”

what happened was that the early cambrian fossils began to undergo a period of criticalreappraisal. fortey and derek briggs—one of the other principals in gould’s book—used amethod known as cladistics to compare the various burgess fossils. in simple terms, cladisticsconsists of organizing organisms on the basis of shared features. fortey gives as an examplethe idea of comparing a shrew and an elephant. if you considered the elephant’s large size andstriking trunk you might conclude that it could have little in common with a tiny, sniffingshrew. but if you compared both of them with a lizard, you would see that the elephant andshrew were in fact built to much the same plan. in essence, what fortey is saying is thatgould saw elephants and shrews where they saw mammals. the burgess creatures, theybelieved, weren’t as strange and various as they appeared at first sight. “they were often nostranger than trilobites,” fortey says now. “it is just that we have had a century or so to getused to trilobites. familiarity, you know, breeds familiarity.”

this wasn’t, i should note, because of sloppiness or inattention. interpreting the forms andrelationships of ancient animals on the basis of often distorted and fragmentary evidence isclearly a tricky business. edward o. wilson has noted that if you took selected species ofmodern insects and presented them as burgess-style fossils nobody would ever guess that theywere all from the same phylum, so different are their body plans. also instrumental in helpingrevisions were the discoveries of two further early cambrian sites, one in greenland and onein china, plus more scattered finds, which between them yielded many additional and oftenbetter specimens.

the upshot is that the burgess fossils were found to be not so different after all.

hallucigenia, it turned out, had been reconstructed upside down. its stilt-like legs wereactually spikes along its back. peytoia, the weird creature that looked like a pineapple slice,was found to be not a distinct creature but merely part of a larger animal called anomalocaris.

many of the burgess specimens have now been assigned to living phyla—just where walcottput them in the first place. hallucigenia and some others are thought to be related toonychophora, a group of caterpillar-like animals. others have been reclassified as precursorsof the modern annelids. in fact, says fortey, “there are relatively few cambrian designs thatare wholly novel. more often they turn out to be just interesting elaborations of well-established designs.” as he wrote in his book life: “none was as strange as a present daybarnacle, nor as grotesque as a queen termite.”

so the burgess shale specimens weren’t so spectacular after all. this made them, as forteyhas written, “no less interesting, or odd, just more explicable.” their weird body plans werejust a kind of youthful exuberance—the evolutionary equivalent, as it were, of spiked hair andtongue studs. eventually the forms settled into a staid and stable middle age.

but that still left the enduring question of where all these animals had come from—howthey had suddenly appeared from out of nowhere.

alas, it turns out the cambrian explosion may not have been quite so explosive as all that.

the cambrian animals, it is now thought, were probably there all along, but were just toosmall to see. once again it was trilobites that provided the clue—in particular that seeminglymystifying appearance of different types of trilobite in widely scattered locations around theglobe, all at more or less the same time.

on the face of it, the sudden appearance of lots of fully formed but varied creatures wouldseem to enhance the miraculousness of the cambrian outburst, but in fact it did the opposite.

it is one thing to have one well-formed creature like a trilobite burst forth in isolation—thatreally is a wonder—but to have many of them, all distinct but clearly related, turning upsimultaneously in the fossil record in places as far apart as china and new york clearlysuggests that we are missing a big part of their history. there could be no stronger evidencethat they simply had to have a forebear—some grandfather species that started the line in amuch earlier past.

and the reason we haven’t found these earlier species, it is now thought, is that they weretoo tiny to be preserved. says fortey: “it isn’t necessary to be big to be a perfectlyfunctioning, complex organism. the sea swarms with tiny arthropods today that have left nofossil record.” he cites the little copepod, which numbers in the trillions in modern seas andclusters in shoals large enough to turn vast areas of the ocean black, and yet our totalknowledge of its ancestry is a single specimen found in the body of an ancient fossilized fish.

“the cambrian explosion, if that’s the word for it, probably was more an increase in sizethan a sudden appearance of new body types,” fortey says. “and it could have happened quiteswiftly, so in that sense i suppose it was an explosion.” the idea is that just as mammalsbided their time for a hundred million years until the dinosaurs cleared off and then seeminglyburst forth in profusion all over the planet, so too perhaps the arthropods and other triploblastswaited in semimicroscopic anonymity for the dominant ediacaran organisms to have theirday. says fortey: “we know that mammals increased in size quite dramatically after thedinosaurs went—though when i say quite abruptly i of course mean it in a geological sense.

we’re still talking millions of years.”

incidentally, reginald sprigg did eventually get a measure of overdue credit. one of themain early genera, spriggina, was named in his honor, as were several species, and the wholebecame known as the ediacaran fauna after the hills through which he had searched. by thistime, however, sprigg’s fossil-hunting days were long over. after leaving geology he foundeda successful oil company and eventually retired to an estate in his beloved flinders range,where he created a wildlife reserve. he died in 1994 a rich man.

22    GOOD-BYE TO ALL THAT

when you consider it from a human perspective, and clearly it would be difficult forus to do otherwise, life is an odd thing. it couldn’t wait to get going, but then, having gottengoing, it seemed in very little hurry to move on.

consider the lichen. lichens are just about the hardiest visible organisms on earth, butamong the least ambitious. they will grow happily enough in a sunny churchyard, but theyparticularly thrive in environments where no other organism would go—on blowymountaintops and arctic wastes, wherever there is little but rock and rain and cold, and almostno competition. in areas of antarctica where virtually nothing else will grow, you can findvast expanses of lichen—four hundred types of them—adhering devotedly to every wind-whipped rock.

for a long time, people couldn’t understand how they did it. because lichens grew on barerock without evident nourishment or the production of seeds, many people—educatedpeople—believed they were stones caught in the process of becoming plants. “spontaneously,inorganic stone becomes living plant!” rejoiced one observer, a dr. homschuch, in 1819.

closer inspection showed that lichens were more interesting than magical. they are in facta partnership between fungi and algae. the fungi excrete acids that dissolve the surface of therock, freeing minerals that the algae convert into food sufficient to sustain both. it is not avery exciting arrangement, but it is a conspicuously successful one. the world has more thantwenty thousand species of lichens.

like most things that thrive in harsh environments, lichens are slow-growing. it may take alichen more than half a century to attain the dimensions of a shirt button. those the size ofdinner plates, writes david attenborough, are therefore “likely to be hundreds if notthousands of years old.” it would be hard to imagine a less fulfilling existence. “they simplyexist,” attenborough adds, “testifying to the moving fact that life even at its simplest leveloccurs, apparently, just for its own sake.”

it is easy to overlook this thought that life just is. as humans we are inclined to feel that lifemust have a point. we have plans and aspirations and desires. we want to take constantadvantage of all the intoxicating existence we’ve been endowed with. but what’s life to alichen? yet its impulse to exist, to be, is every bit as strong as ours—arguably even stronger.

if i were told that i had to spend decades being a furry growth on a rock in the woods, ibelieve i would lose the will to go on. lichens don’t. like virtually all living things, they willsuffer any hardship, endure any insult, for a moment’s additional existence. life, in short, justwants to be. but—and here’s an interesting point—for the most part it doesn’t want to bemuch.

this is perhaps a little odd because life has had plenty of time to develop ambitions. if youimagine the 4,500-billion-odd years of earth’s history compressed into a normal earthly day,then life begins very early, about 4a.m., with the rise of the first simple, single-celled
organisms, but then advances no further for the next sixteen hours. not until almost 8:30 inthe evening, with the day five-sixths over, has earth anything to show the universe but arestless skin of microbes. then, finally, the first sea plants appear, followed twenty minuteslater by the first jellyfish and the enigmatic ediacaran fauna first seen by reginald sprigg inaustralia. at 9:04p.m. trilobites swim onto the scene, followed more or less immediately bythe shapely creatures of the burgess shale. just before 10p.m. plants begin to pop up on theland. soon after, with less than two hours left in the day, the first land creatures follow.

thanks to ten minutes or so of balmy weather, by 10:24 the earth is covered in the greatcarboniferous forests whose residues give us all our coal, and the first winged insects areevident. dinosaurs plod onto the scene just before 11p.m. and hold sway for about three-quarters of an hour. at twenty-one minutes to midnight they vanish and the age of mammalsbegins. humans emerge one minute and seventeen seconds before midnight. the whole of ourrecorded history, on this scale, would be no more than a few seconds, a single human lifetimebarely an instant. throughout this greatly speeded-up day continents slide about and bangtogether at a clip that seems positively reckless. mountains rise and melt away, ocean basinscome and go, ice sheets advance and withdraw. and throughout the whole, about three timesevery minute, somewhere on the planet there is a flashbulb pop of light marking the impact ofa manson-sized meteor or one even larger. it’s a wonder that anything at all can survive insuch a pummeled and unsettled environment. in fact, not many things do for long.

perhaps an even more effective way of grasping our extreme recentness as a part of this4.5-billion-year-old picture is to stretch your arms to their fullest extent and imagine thatwidth as the entire history of the earth. on this scale, according to john mcphee in basin andrange, the distance from the fingertips of one hand to the wrist of the other is precambrian.

all of complex life is in one hand, “and in a single stroke with a medium-grained nail file youcould eradicate human history.”

fortunately, that moment hasn’t happened, but the chances are good that it will. i don’twish to interject a note of gloom just at this point, but the fact is that there is one otherextremely pertinent quality about life on earth: it goes extinct. quite regularly. for all thetrouble they take to assemble and preserve themselves, species crumple and die remarkablyroutinely. and the more complex they get, the more quickly they appear to go extinct. whichis perhaps one reason why so much of life isn’t terribly ambitious.

so anytime life does something bold it is quite an event, and few occasions were moreeventful than when life moved on to the next stage in our narrative and came out of the sea.

land was a formidable environment: hot, dry, bathed in intense ultraviolet radiation,lacking the buoyancy that makes movement in water comparatively effortless. to live onland, creatures had to undergo wholesale revisions of their anatomies. hold a fish at each endand it sags in the middle, its backbone too weak to support it. to survive out of water, marinecreatures needed to come up with new load-bearing internal architecture—not the sort ofadjustment that happens overnight. above all and most obviously, any land creature wouldhave to develop a way to take its oxygen directly from the air rather than filter it from water.

these were not trivial challenges to overcome. on the other hand, there was a powerfulincentive to leave the water: it was getting dangerous down there. the slow fusion of thecontinents into a single landmass, pangaea, meant there was much, much less coastline thanformerly and thus much less coastal habitat. so competition was fierce. there was also an
omnivorous and unsettling new type of predator on the scene, one so perfectly designed forattack that it has scarcely changed in all the long eons since its emergence: the shark. neverwould there be a more propitious time to find an alternative environment to water.

plants began the process of land colonization about 450 million years ago, accompanied ofnecessity by tiny mites and other organisms that they needed to break down and recycle deadorganic matter on their behalf. larger animals took a little longer to emerge, but by about 400million years ago they were venturing out of the water, too. popular illustrations haveencouraged us to envision the first venturesome land dwellers as a kind of ambitious fish—something like the modern mudskipper, which can hop from puddle to puddle duringdroughts—or even as a fully formed amphibian. in fact, the first visible mobile residents ondry land were probably much more like modern wood lice, sometimes also known as pillbugsor sow bugs. these are the little bugs (crustaceans, in fact) that are commonly thrown intoconfusion when you upturn a rock or log.

for those that learned to breathe oxygen from the air, times were good. oxygen levels inthe devonian and carboniferous periods, when terrestrial life first bloomed, were as high as35 percent (as opposed to nearer 20 percent now). this allowed animals to grow remarkablylarge remarkably quickly.

and how, you may reasonably wonder, can scientists know what oxygen levels were likehundreds of millions of years ago? the answer lies in a slightly obscure but ingenious fieldknown as isotope geochemistry. the long-ago seas of the carboniferous and devonianswarmed with tiny plankton that wrapped themselves inside tiny protective shells. then, asnow, the plankton created their shells by drawing oxygen from the atmosphere and combiningit with other elements (carbon especially) to form durable compounds such as calciumcarbonate. it’s the same chemical trick that goes on in (and is discussed elsewhere in relationto) the long-term carbon cycle—a process that doesn’t make for terribly exciting narrative butis vital for creating a livable planet.

eventually in this process all the tiny organisms die and drift to the bottom of the sea,where they are slowly compressed into limestone. among the tiny atomic structures theplankton take to the grave with them are two very stable isotopes—oxygen-16 and oxygen-18.

(if you have forgotten what an isotope is, it doesn’t matter, though for the record it’s an atomwith an abnormal number of neutrons.) this is where the geochemists come in, for theisotopes accumulate at different rates depending on how much oxygen or carbon dioxide is inthe atmosphere at the time of their creation. by comparing these ancient ratios, thegeochemists can cunningly read conditions in the ancient world—oxygen levels, air and oceantemperatures, the extent and timing of ice ages, and much else. by combining their isotopefindings with other fossil residues—pollen levels and so on—scientists can, with considerableconfidence, re-create entire landscapes that no human eye ever saw.

the principal reason oxygen levels were able to build up so robustly throughout the periodof early terrestrial life was that much of the world’s landscape was dominated by giant treeferns and vast swamps, which by their boggy nature disrupted the normal carbon recyclingprocess. instead of completely rotting down, falling fronds and other dead vegetative matteraccumulated in rich, wet sediments, which were eventually squeezed into the vast coal bedsthat sustain much economic activity even now.

the heady levels of oxygen clearly encouraged outsized growth. the oldest indication of asurface animal yet found is a track left 350 million years ago by a millipede-like creature on a
rock in scotland. it was over three feet long. before the era was out some millipedes wouldreach lengths more than double that.

with such creatures on the prowl, it is perhaps not surprising that insects in the periodevolved a trick that could keep them safely out of tongue shot: they learned to fly. some tookto this new means of locomotion with such uncanny facility that they haven’t changed theirtechniques in all the time since. then, as now, dragonflies could cruise at up to thirty-fivemiles an hour, instantly stop, hover, fly backwards, and lift far more proportionately than anyhuman flying machine. “the u.s. air force,” one commentator has written, “has put them inwind tunnels to see how they do it, and despaired.” they, too, gorged on the rich air. incarboniferous forests dragonflies grew as big as ravens. trees and other vegetation likewiseattained outsized proportions. horsetails and tree ferns grew to heights of fifty feet, clubmosses to a hundred and thirty.

the first terrestrial vertebrates—which is to say, the first land animals from which wewould derive—are something of a mystery. this is partly because of a shortage of relevantfossils, but partly also because of an idiosyncratic swede named erik jarvik whose oddinterpretations and secretive manner held back progress on this question for almost half acentury. jarvik was part of a team of scandinavian scholars who went to greenland in the1930s and 1940s looking for fossil fish. in particular they sought lobe-finned fish of the typethat presumably were ancestral to us and all other walking creatures, known as tetrapods.

most animals are tetrapods, and all living tetrapods have one thing in common: four limbsthat end in a maximum of five fingers or toes. dinosaurs, whales, birds, humans, even fish—all are tetrapods, which clearly suggests they come from a single common ancestor. the clueto this ancestor, it was assumed, would be found in the devonian era, from about 400 millionyears ago. before that time nothing walked on land. after that time lots of things did. luckilythe team found just such a creature, a three-foot-long animal called an ichthyostega. theanalysis of the fossil fell to jarvik, who began his study in 1948 and kept at it for the nextforty-eight years. unfortunately, jarvik refused to let anyone study his tetrapod. the world’spaleontologists had to be content with two sketchy interim papers in which jarvik noted thatthe creature had five fingers in each of four limbs, confirming its ancestral importance.

jarvik died in 1998. after his death, other paleontologists eagerly examined the specimenand found that jarvik had severely miscounted the fingers and toes—there were actually eighton each limb—and failed to observe that the fish could not possibly have walked. thestructure of the fin was such that it would have collapsed under its own weight. needless tosay, this did not do a great deal to advance our understanding of the first land animals. todaythree early tetrapods are known and none has five digits. in short, we don’t know quite wherewe came from.

but come we did, though reaching our present state of eminence has not of course alwaysbeen straightforward. since life on land began, it has consisted of four megadynasties, as theyare sometimes called. the first consisted of primitive, plodding but sometimes fairly heftyamphibians and reptiles. the best-known animal of this age was the dimetrodon, a sail-backed creature that is commonly confused with dinosaurs (including, i note, in a picturecaption in the carl sagan book comet). the dimetrodon was in fact a synapsid. so, onceupon a time, were we. synapsids were one of the four main divisions of early reptilian life,the others being anapsids, euryapsids, and diapsids. the names simply refer to the number andlocation of small holes to be found in the sides of their owners’ skulls. synapsids had one holein their lower temples; diapsids had two; euryapsids had a single hole higher up.

over time, each of these principal groupings split into further subdivisions, of which someprospered and some faltered. anapsids gave rise to the turtles, which for a time, perhaps atouch improbably, appeared poised to predominate as the planet’s most advanced and deadlyspecies, before an evolutionary lurch let them settle for durability rather than dominance. thesynapsids divided into four streams, only one of which survived beyond the permian.

happily, that was the stream we belonged to, and it evolved into a family of protomammalsknown as therapsids. these formed megadynasty 2.

unfortunately for the therapsids, their cousins the diapsids were also productively evolving,in their case into dinosaurs (among other things), which gradually proved too much for thetherapsids. unable to compete head to head with these aggressive new creatures, thetherapsids by and large vanished from the record. a very few, however, evolved into small,furry, burrowing beings that bided their time for a very long while as little mammals. thebiggest of them grew no larger than a house cat, and most were no bigger than mice.

eventually, this would prove their salvation, but they would have to wait nearly 150 millionyears for megadynasty 3, the age of dinosaurs, to come to an abrupt end and make room formegadynasty 4 and our own age of mammals.

each of these massive transformations, as well as many smaller ones between and since,was dependent on that paradoxically important motor of progress: extinction. it is a curiousfact that on earth species death is, in the most literal sense, a way of life. no one knows howmany species of organisms have existed since life began. thirty billion is a commonly citedfigure, but the number has been put as high as 4,000 billion. whatever the actual total, 99.99percent of all species that have ever lived are no longer with us. “to a first approximation,” asdavid raup of the university of chicago likes to say, “all species are extinct.” for complexorganisms, the average lifespan of a species is only about four million years—roughly aboutwhere we are now.

extinction is always bad news for the victims, of course, but it appears to be a good thingfor a dynamic planet. “the alternative to extinction is stagnation,” says ian tattersall of theamerican museum of natural history, “and stagnation is seldom a good thing in any realm.”

(i should perhaps note that we are speaking here of extinction as a natural, long-term process.

extinction brought about by human carelessness is another matter altogether.)crises in earth’s history are invariably associated with dramatic leaps afterward. the fall ofthe ediacaran fauna was followed by the creative outburst of the cambrian period. theordovician extinction of 440 million years ago cleared the oceans of a lot of immobile filterfeeders and, somehow, created conditions that favored darting fish and giant aquatic reptiles.

these in turn were in an ideal position to send colonists onto dry land when another blowoutin the late devonian period gave life another sound shaking. and so it has gone at scatteredintervals through history. if most of these events hadn’t happened just as they did, just whenthey did, we almost certainly wouldn’t be here now.

earth has seen five major extinction episodes in its time—the ordovician, devonian,permian, triassic, and cretaceous, in that order—and many smaller ones. the ordovician(440 million years ago) and devonian (365 million) each wiped out about 80 to 85 percent ofspecies. the triassic (210 million years ago) and cretaceous (65 million years) each wipedout 70 to 75 percent of species. but the real whopper was the permian extinction of about 245million years ago, which raised the curtain on the long age of the dinosaurs. in the permian, at
least 95 percent of animals known from the fossil record check out, never to return. evenabout a third of insect species went—the only occasion on which they were lost en masse. it isas close as we have ever come to total obliteration.

“it was, truly, a mass extinction, a carnage of a magnitude that had never troubled the earthbefore,” says richard fortey. the permian event was particularly devastating to sea creatures.

trilobites vanished altogether. clams and sea urchins nearly went. virtually all other marineorganisms were staggered. altogether, on land and in the water, it is thought that earth lost 52percent of its families—that’s the level above genus and below order on the grand scale of life(the subject of the next chapter)—and perhaps as many as 96 percent of all its species. itwould be a long time—as much as eighty million years by one reckoning—before speciestotals recovered.

two points need to be kept in mind. first, these are all just informed guesses. estimates forthe number of animal species alive at the end of the permian range from as low as 45,000 toas high as 240,000. if you don’t know how many species were alive, you can hardly specifywith conviction the proportion that perished. moreover, we are talking about the death ofspecies, not individuals. for individuals the death toll could be much higher—in many cases,practically total. the species that survived to the next phase of life’s lottery almost certainlyowe their existence to a few scarred and limping survivors.

in between the big kill-offs, there have also been many smaller, less well-known extinctionepisodes—the hemphillian, frasnian, famennian, rancholabrean, and a dozen or so others—which were not so devastating to total species numbers, but often critically hit certainpopulations. grazing animals, including horses, were nearly wiped out in the hemphillianevent about five million years ago. horses declined to a single species, which appears sosporadically in the fossil record as to suggest that for a time it teetered on the brink ofoblivion. imagine a human history without horses, without grazing animals.

in nearly every case, for both big extinctions and more modest ones, we have bewilderinglylittle idea of what the cause was. even after stripping out the more crackpot notions there arestill more theories for what caused the extinction events than there have been events. at leasttwo dozen potential culprits have been identified as causes or prime contributors: globalwarming, global cooling, changing sea levels, oxygen depletion of the seas (a conditionknown as anoxia), epidemics, giant leaks of methane gas from the seafloor, meteor and cometimpacts, runaway hurricanes of a type known as hypercanes, huge volcanic upwellings,catastrophic solar flares.

this last is a particularly intriguing possibility. nobody knows how big solar flares can getbecause we have only been watching them since the beginning of the space age, but the sun isa mighty engine and its storms are commensurately enormous. a typical solar flare—something we wouldn’t even notice on earth—will release the energy equivalent of a billionhydrogen bombs and fling into space a hundred billion tons or so of murderous high-energyparticles. the magnetosphere and atmosphere between them normally swat these back intospace or steer them safely toward the poles (where they produce the earth’s comely auroras),but it is thought that an unusually big blast, say a hundred times the typical flare, couldoverwhelm our ethereal defenses. the light show would be a glorious one, but it would almostcertainly kill a very high proportion of all that basked in its glow. moreover, and ratherchillingly, according to bruce tsurutani of the nasa jet propulsion laboratory, “it wouldleave no trace in history.”

what all this leaves us with, as one researcher has put it, is “tons of conjecture and verylittle evidence.” cooling seems to be associated with at least three of the big extinctionevents—the ordovician, devonian, and permian—but beyond that little is agreed, includingwhether a particular episode happened swiftly or slowly. scientists can’t agree, for instance,whether the late devonian extinction—the event that was followed by vertebrates movingonto the land—happened over millions of years or thousands of years or in one lively day.

one of the reasons it is so hard to produce convincing explanations for extinctions is that itis so very hard to exterminate life on a grand scale. as we have seen from the manson impact,you can receive a ferocious blow and still stage a full, if presumably somewhat wobbly,recovery. so why, out of all the thousands of impacts earth has endured, was the kt event sosingularly devastating? well, first itwas positively enormous. it struck with the force of 100million megatons. such an outburst is not easily imagined, but as james lawrence powell haspointed out, if you exploded one hiroshima-sized bomb for every person alive on earth todayyou would still be about a billion bombs short of the size of the kt impact. but even thatalone may not have been enough to wipe out 70 percent of earth’s life, dinosaurs included.

the kt meteor had the additional advantage—advantage if you are a mammal, that is—that it landed in a shallow sea just ten meters deep, probably at just the right angle, at a timewhen oxygen levels were 10 percent higher than at present and so the world was morecombustible. above all the floor of the sea where it landed was made of rock rich in sulfur.

the result was an impact that turned an area of seafloor the size of belgium into aerosols ofsulfuric acid. for months afterward, the earth was subjected to rains acid enough to burn skin.

in a sense, an even greater question than that of what wiped out 70 percent of the speciesthat were existing at the time is how did the remaining 30 percent survive? why was the eventso irremediably devastating to every single dinosaur that existed, while other reptiles, likesnakes and crocodiles, passed through unimpeded? so far as we can tell no species of toad,newt, salamander, or other amphibian went extinct in north america. “why should thesedelicate creatures have emerged unscathed from such an unparalleled disaster?” asks timflannery in his fascinating prehistory of america, eternal frontier.

in the seas it was much the same story. all the ammonites vanished, but their cousins thenautiloids, who lived similar lifestyles, swam on. among plankton, some species werepractically wiped out—92 percent of foraminiferans, for instance—while other organisms likediatoms, designed to a similar plan and living alongside, were comparatively unscathed.

these are difficult inconsistencies. as richard fortey observes: “somehow it does notseem satisfying just to call them ‘lucky ones’ and leave it at that.” if, as seems entirely likely,the event was followed by months of dark and choking smoke, then many of the insectsurvivors become difficult to account for. “some insects, like beetles,” fortey notes, “couldlive on wood or other things lying around. but what about those like bees that navigate bysunlight and need pollen? explaining their survival isn’t so easy.”

above all, there are the corals. corals require algae to survive and algae require sunlight,and both together require steady minimum temperatures. much publicity has been given in thelast few years to corals dying from changes in sea temperature of only a degree or so. if theyare that vulnerable to small changes, how did they survive the long impact winter?

there are also many hard-to-explain regional variations. extinctions seem to have been farless severe in the southern hemisphere than the northern. new zealand in particular appears to
have come through largely unscathed even though it had almost no burrowing creatures. evenits vegetation was overwhelmingly spared, and yet the scale of conflagration elsewheresuggests that devastation was global. in short, there is just a great deal we don’t know.

some animals absolutely prospered—including, a little surprisingly, the turtles once again.

as flannery notes, the period immediately after the dinosaur extinction could well be knownas the age of turtles. sixteen species survived in north america and three more came intoexistence soon after.

clearly it helped to be at home in water. the kt impact wiped out almost 90 percent ofland-based species but only 10 percent of those living in fresh water. water obviously offeredprotection against heat and flame, but also presumably provided more sustenance in the leanperiod that followed. all the land-based animals that survived had a habit of retreating to asafer environment during times of danger—into water or underground—either of whichwould have provided considerable shelter against the ravages without. animals thatscavenged for a living would also have enjoyed an advantage. lizards were, and are, largelyimpervious to the bacteria in rotting carcasses. indeed, often they are positively drawn to it,and for a long while there were clearly a lot of putrid carcasses about.

it is often wrongly stated that only small animals survived the kt event. in fact, among thesurvivors were crocodiles, which were not just large but three times larger than they are today.

but on the whole, it is true, most of the survivors were small and furtive. indeed, with theworld dark and hostile, it was a perfect time to be small, warm-blooded, nocturnal, flexible indiet, and cautious by nature—the very qualities that distinguished our mammalian forebears.

had our evolution been more advanced, we would probably have been wiped out. instead,mammals found themselves in a world to which they were as well suited as anything alive.

however, it wasn’t as if mammals swarmed forward to fill every niche. “evolution mayabhor a vacuum,” wrote the paleobiologist steven m. stanley, “but it often takes a long timeto fill it.” for perhaps as many as ten million years mammals remained cautiously small. inthe early tertiary, if you were the size of a bobcat you could be king.

but once they got going, mammals expanded prodigiously—sometimes to an almostpreposterous degree. for a time, there were guinea pigs the size of rhinos and rhinos the sizeof a two-story house. wherever there was a vacancy in the predatory chain, mammals rose(often literally) to fill it. early members of the raccoon family migrated to south america,discovered a vacancy, and evolved into creatures the size and ferocity of bears. birds, too,prospered disproportionately. for millions of years, a gigantic, flightless, carnivorous birdcalled titanis was possibly the most ferocious creature in north america. certainly it was themost daunting bird that ever lived. it stood ten feet high, weighed over eight hundred pounds,and had a beak that could tear the head off pretty much anything that irked it. its familysurvived in formidable fashion for fifty million years, yet until a skeleton was discovered inflorida in 1963, we had no idea that it had ever existed.

which brings us to another reason for our uncertainty about extinctions: the paltriness ofthe fossil record. we have touched already on the unlikelihood of any set of bones becomingfossilized, but the record is actually worse than you might think. consider dinosaurs.

museums give the impression that we have a global abundance of dinosaur fossils. in fact,overwhelmingly museum displays are artificial. the giant diplodocus that dominates theentrance hall of the natural history museum in london and has delighted and informedgenerations of visitors is made of plaster—built in 1903 in pittsburgh and presented to the
museum by andrew carnegie. the entrance hall of the american museum of natural historyin new york is dominated by an even grander tableau: a skeleton of a large barosaurusdefending her baby from attack by a darting and toothy allosaurus. it is a wonderfullyimpressive display—the barosaurus rises perhaps thirty feet toward the high ceiling—but alsoentirely fake. every one of the several hundred bones in the display is a cast. visit almost anylarge natural history museum in the world—in paris, vienna, frankfurt, buenos aires,mexico city—and what will greet you are antique models, not ancient bones.

the fact is, we don’t really know a great deal about the dinosaurs. for the whole of the ageof dinosaurs, fewer than a thousand species have been identified (almost half of them knownfrom a single specimen), which is about a quarter of the number of mammal species alivenow. dinosaurs, bear in mind, ruled the earth for roughly three times as long as mammalshave, so either dinosaurs were remarkably unproductive of species or we have barelyscratched the surface (to use an irresistibly apt cliché).

for millions of years through the age of dinosaurs not a single fossil has yet been found.

even for the period of the late cretaceous—the most studied prehistoric period there is,thanks to our long interest in dinosaurs and their extinction—some three quarters of allspecies that lived may yet be undiscovered. animals bulkier than the diplodocus or moreforbidding than tyrannosaurus may have roamed the earth in the thousands, and we maynever know it. until very recently everything known about the dinosaurs of this period camefrom only about three hundred specimens representing just sixteen species. the scantiness ofthe record led to the widespread belief that dinosaurs were on their way out already when thekt impact occurred.

in the late 1980s a paleontologist from the milwaukee public museum, peter sheehan,decided to conduct an experiment. using two hundred volunteers, he made a painstakingcensus of a well-defined, but also well-picked-over, area of the famous hell creek formationin montana. sifting meticulously, the volunteers collected every last tooth and vertebra andchip of bone—everything that had been overlooked by previous diggers. the work took threeyears. when finished they found that they had more than tripled the global total of dinosaurfossils from the late cretaceous. the survey established that dinosaurs remained numerousright up to the time of the kt impact. “there is no reason to believe that the dinosaurs weredying out gradually during the last three million years of the cretaceous,” sheehan reported.

we are so used to the notion of our own inevitability as life’s dominant species that it ishard to grasp that we are here only because of timely extraterrestrial bangs and other randomflukes. the one thing we have in common with all other living things is that for nearly fourbillion years our ancestors have managed to slip through a series of closing doors every timewe needed them to. stephen jay gould expressed it succinctly in a well-known line: “humansare here today because our particular line never fractured—never once at any of the billionpoints that could have erased us from history.”

we started this chapter with three points: life wants to be; life doesn’t always want to bemuch; life from time to time goes extinct. to this we may add a fourth: life goes on. andoften, as we shall see, it goes on in ways that are decidedly amazing.