from a ive, and clearly it    forus to do ot couldn’t    to get going, but ttengoing, it seemed in very little o move on.

        sider t about t visible anisms oamong t ambitious. t ticularly ts ops and arctic es,    rod rain and cold, and almostno petition. In areas of Antarctica    expanses of licypes of tedly to every wind-whipped rock.

        For a long time, people couldn’t uand . Because lic evident nouris or tion of seeds, many people—educatedpeople—believed tones caugs. “Spontaneously,inanic stone bees living plant!” rejoiced one observer, a Dr. homschuch, in 1819.

        Closer iion s liceresting ta partnerse acids t dissolve t t into food suffit to sustain bot is not avery exg arra, but it is a spicuously successful oy thousand species of lis.

        Like most t ts, lic may take alicury to attain t button. tes, es David Attenbo be t e,” Attenbestifying to t t life even at its simplest leveloccurs, apparently, just for its own sake.”

        It is easy to overlook t t life just is. As o feel t lifemust . e ions and desires. e    to take stantadvantage of all toxig existence    o alic its impulse to exist, to be, is every bit as strong as ours—arguably even stronger.

        If I old t I o spend decades being a furry groually all living t, for a moment’s additioence. Life, in s, justs to be. But—aing point—for t part it doesn’t    to bemuch.

        ttle odd because life y of time to develop ambitions. If youimagiory pressed into a normal eart 4A.M.,    simple, single-celledanisms, but t sixteen    until almost 8:30 into s arestless skin of microbes. t sea plants appear, folloy mier by t jellyfisic Edia fauna first seen by Reginald Sprigg inAustralia. At 9:04P.M. trilobites so tely bytures of t before 10P.M. plants begin to pop up on ter,    land creatures follow.

        to ten minutes or so of balmy carboniferous forests s areevident. Dinosaurs plod onto t before 11P.M. and    ters of an    ty-one mio midnige aeen seds before midnigory, on timebarely an instant. t tly speeded-up day tis slide about and bangtoget a clip t seems positively reckless. Mountains rise a a t timesevery minute, some marking t ofa Manson-sized meteor or one even larger. It’s a    anyt all    survive insuctled enviro. In faot many things do for long.

        Perive reme reess as a part of ture is to stretco t extent and imagiire ory of to Joance from tips of o of ther is Precambrian.

        All of plex life is in one roke e ory.”

        Fortunately, t moment     t it erject a note of gloom just at t, but t is t tremely perti quality about life o goes extinct. Quite regularly. For all trouble take to assemble and preserve tinely. And t, to go extinct.    terribly ambitious.

        So anytime life does somet is quite a, and feful to t stage in our narrative and came out of the sea.

        Land : , dry, bateraviolet radiation,lag t makes movement in er paratively effortless. to live onland, creatures o undergo s bae too o support it. to survive out of er, mariures o e up ernal arcecture—not t ofadjustment t . Above all and most obviously, any land creature o take its oxygen directly from ter it from er.

        t trivial co overe. On tive to leave ter: it ting dangerous dois into a single landmass, Pangaea, meant tlial at. So petition tling neype of predator on tly designed forattack t it s emergeious time to find an alternative enviroo er.

        Plants began tion about 450 million years ago, apanied ofy by tiny mites and ot to break doter on took a little loo emerge, but by about 400million years ag out of ter, too. Popular illustrations o envision t venturesome land dious fiso puddle duringdroug, t visible mobile residents ondry land tle bugs (crustas, in fact) t are only tofusion wurn a rock .

        For t learo breatimes errestrial life first bloomed, o nearer 20 pert noo grow remarkablylarge remarkably quickly.

        And ists kno ingenious fieldknoope geocry. tiny plankton t iny protective soed tmosp s (carbon especially) to form durable pounds suce. It’s trick t goes on in (and is discussed elseo) term carbon cycle—a process t doesn’t make for terribly exg narrative butis vital for creating a livable pla.

        Eventually in tiny anisms die and drift to ttom of to limestone. Among tiny atomic structures ton take to table isotopes—oxygen-16 and oxygen-18.

        (If you ten ope is, it doesn’t matter, t’s an atomrons.) ts e in, for topes accumulate at different rates depending on mosp time of tion. By paring t ratios, ts    ingly read ditions in t emperatures, tent and timing of ice ages, and mucopefindings ists , e entire landscapes t no human eye ever saw.

        to build up so robustly t terrestrial life    muced by giant treeferns and vast sed tead of pletely rotting doative matteraccumulated in ric sediments, o t coal bedst sustain mucivity even now.

        tsized groion of asurfaimal yet found is a track left 350 million years ago by a millipede-like creature on aro Scotland. It    long. Before t some millipedes wouldreac.

        itures on t is per surprising t is in trick t could keep t of tongue s: to fly. Some tookto tion y t t cecime si up to ty-fivemiles an antly stop,    far more proportioator ten, “ tuo see , and despaired.” too, ged on ts dragonflies grerees and otation liketained outsized proportions. ails and tree ferns greo s of fifty feet, clubmosses to a y.

        t terrestrial vertebrates— land animals from ly because of a sage of relevantfossils, but partly also because of an idiosyncratic Sations aive manner ion for almost ury. Jarvik    of a team of Sdinavian sc to Greenland in ticular t lobe-finned fisypet presumably ral to us and all otures, krapods.

        Most animals are tetrapods, and all livirapods    end in a maximum of five fingers or toes. Dinosaurs, rapods, or. to tor, it    400 millionyears ago. Before t time    time lots of team found just sucure, a t-long animal called an Icega. to Jarvik,    at it for tforty-eigunately, Jarvik refused to let audy etrapod. tologists o be tent cerim papers in ture s aral importance.

        Jarvik died in 1998. After ologists eagerly exami Jarvik ed toes—tually eigo observe t t possibly ructure of t it    do a great deal to advance our uanding of t land animals. todaytetrapods are kno knoe wherewe came from.

        But e    state of eminence    of course alraig ed of fadynasties, as times called. t sisted of primitive, plodding but sometimes fairly yampiles. t-knorodon, a sail-backed creature t is only fused e, in a picturecaption in t). trodon    a synapsid. So, onceupon a time, ilian life,to tion of small o be found in temples; diapsids wo; euryapsids had a single hole higher up.

        Over time, eato furtered. Anapsids gave rise to turtles, e as t’s most advanced and deadlyspecies, before an evolutionary lurc ttle for durability rato four streams, only one of whe Permian.

        ream o, and it evolved into a family of protomammalsknoy 2.

        Unfortunately for tively evolving,in to dinosaurs (among otoo mupete o ures, to small,furry, burro bided time for a very long    of t, and most han mice.

        Eventually, tion, but to    nearly 150 millionyears fadynasty 3, to e to an abrupt end and make room fadynasty 4 and our own Age of Mammals.

        Easformations, as    on t paradoxically important motor ress: extin. It is a curiousfact t o literal sense, a y billion is a only citedfigure, but t as ever tual total, 99.99pert of all species t o a first approximation,” asDavid Raup of ty of Co say, “all species are extinct.” For plexanisms, t four million years—rougwhere we are now.

        Extin is alims, of course, but it appears to be a good t. “ternative to extin is stagnation,” says Ian tattersall of tural ory, “and stagnation is seldom a good thing in any realm.”

        (I se t ion as a natural, long-term process.

        Extin broug by ter altogetory are invariably associated ic leaps afterive outburst of tin of 440 million years ago cleared t of immobile filterfeeders and, someed ditions t favored darting fis aquatic reptiles.

        turn ion to send ists onto dry land e Devonian period gave life anot    scatteredintervals tory. If most of ts     as t ainly    be here now.

        Eartin episodes in its time—triassid Cretaceous, in t order—and many smaller o about 80 to 85 pert ofspecies. triassic (210 million years ago) and Cretaceous (65 million years) eac 70 to 75 pert of species. But tin of about 245million years ago, least 95 pert of animals kno, o return. Evenabout a t species —t en masse. It isas close as otal obliteration.

        “It ruly, a mass extin, a age of a magnitude t roubled tey. t icularly devastating to sea creatures.

        trilobites vanisoget. Virtually all otaggered. Altogeter, it is t t Eart 52pert of its families—t’s t of t cer)—and per of all its species. Itime—as mucy million years by one reing—before speciestotals recovered.

        ts o be kept in mind. First, t informed guesses. Estimates fort toas    knoion t perisalking about t individuals. For individuals toll could be mucically total. t survived to t ptery almost certainlyoeo a few scarred and limping survivors.

        Iinepisodes—t so devastating to total species numbers, but often critically    certainpopulations. Grazing animals, including    in t about five million years ago. o a single species,    t for a time it teetered on tory     grazing animals.

        In nearly every case, for botins and more modest ones, le idea of er stripping out t notions till more t caused tin events ts. At leasttential culprits ified as causes or prime tributlobalionkno leaks of meteor and etimpacts, runarophic solar flares.

        t is a particularly intriguing possibility. Nobody knoy engine and its storms are ensurately enormous. A typical solar flare—somet even noti Eart of a billiono space a ons or so of murderous icles. tospmosp tospace or steer to it is t t an unusually big blast, say a imes typical flare, couldover certainly kill a very ion of all t basked in its gloo Bruce tsurutani of t Propulsion Laboratory, “it ra ory.”

        all t it, is “tons of jecture and verylittle evidence.” Cooling seems to be associated    least tinevents—t beyond t little is agreed, includingists ’t agree, for instan—t t ebrates movingonto thousands of years or in one lively day.

        One of t is so o produce ving explanations for extins is t itis so very o exterminate life on a grand scale. As ill stage a full, if presumably somes Eart event sosingularly devastating? ell, first itively enormous. It strus. Sucburst is not easily imagined, but as James La, if you exploded one odayyou ill be about a billion bombs s of t impact. But even talone may not o    70 pert of Earth’s life, dinosaurs included.

        t meteor ional advantage—advantage if you are a mammal, t is—t it landed in a s teers deep, probably at just t a a time and so tible. Above all t landed was made of rock ri sulfur.

        t    t turned an area of seafloor to aerosols ofsulfuric acid. For moo rains acid enougo burn skin.

        In a sense, an eveer question t of    70 pert of t ing at time is    survive? so irremediably devastating to every single dinosaur t existed, ell no species of toad,in Norte creatures er?” asks timFlannery in ing preory of America, Eternal Frontier.

        In t es vanis tiloids, on, some species ically —92 pert of foraminiferans, for instance—o a similar plan and living alongside, ively unscathed.

        t insistencies. As Ricey observes: “Some does notseem satisfying just to call t at t.” If, as seems entirely likely,t survivors bee difficult to at for. “Some is, like beetles,” Fortey notes, “couldlive on     t navigate bysunlig so easy.”

        Above all, to survive and algae require sunligogeteady minimum temperatures. Mucy    feo corals dying from cemperature of only a degree or so. If t vulnerable to small c er?

        to-explain regional variatioins seem to icular appears to    no burroures. Evenits vegetation ion else devastation    a great deal    know.

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

        As Flannery ely after tin could urtles. Sixteen species survived in Nortoexistence soon after.

        Clearly it o be at er. t impact    almost 90 pert ofland-based species but only 10 pert of ter. ater obviously offeredprote against    and flame, but also presumably provided more sustenan t follo survived    of retreating to asafer enviro during times of danger—into er or undergrouer against t. Animals tsged for a living o teria in rotting carcasses. Indeed, often tively drao it,and for a long rid carcasses about.

        It is ofte only small animals survived t event. In fact, among t just large but times larger today.

        But on t is true, most of tive. Indeed, ile, it    time to be small, urnal, flexible i, and cautious by nature—ties t distinguished our mammalian forebears.

        ion been more advanced, ead,mammals found to hing alive.

        as if mammals so fill every niayabe t Steven M. Stanley, “but it often takes a long timeto fill it.” For peren million years mammals remained cautiously small. Iiary, if you    you could be king.

        But o going, mammals expanded prodigiously—sometimes to an almostpreposterous degree. For a time, tory ory    literally) to fill it. Early members of ted to Souto creatures ty of bears. Birds, too,prospered disproportionately. For millions of years, a gigantic, fligitanis    ferocious creature in Nortainly it    daunting bird t ever lived. It stood te     could tear tty muc irked it. Its familysurvived in formidable fasy million years, yet until a skeleton    ed.

        o anotainty about extins: triness oftouc of bones beingfossilized, but tually    think. sider dinosaurs.

        Museums give t    Diplodocus t domirance ural ory Museum in London and ed and infeions of visitors is made of plaster—built in 1903 in Pittsburged to trance ural oryin Need by an even graableau: a skeleton of a large Barosaurusdefending tack by a darting and toot is a y feet to alsoentirely fake. Every one of t. Visit almost anylarge natural ory museum in t, Buenos Aires,Mexico City—and    you are antique models, not a bones.

        t is,    really kno deal about tified (almost    a quarter of times as long as mammalsive of species or ibly apt cliché).

        For millions of years t a single fossil    been found.

        Even for te Cretaceous—t studied preoric period to our long i in dinosaurs and tin—some ters of allspecies t lived may yet be undiscovered. Animals bulkier tyrannosaurus may . Until very retly everyt t ting just sixteen species. tiness ofto t dinosaurs    already    occurred.

        In te 1980s a paleontologist from ter So du experiment. Using t also ionin Montana. Siftiiculously, teers collected every last tootebra andc ook t tripled total of dinosaurfossils from te Cretaceous. tablis dinosaurs remained numero time of t impact. “to believe t t gradually during t taceous,” Sed.

        e are so used to tion of our oability as life’s dominant species t it iso grasp t raterrestrial bangs and ot for nearly fourbillion years our aors o slip timeo. Step suctly in a icular line never fractured—never o any of ts t could ory.”

        e started ter s: Life s to be; life doesn’t al to bemucime to time goes extinct. to ten, as    are decidedly amazing.
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