IN t named Mike V around onsome grassy farmland iern Nebraska, not far from ttle toed a curious glint in to    ly preserved skull ofa young r by ret heavy rains.

        A fe turned out,    extraordinary fossil beds everdiscovered in Norter    ooturtles. All erious cataclysm just uime knoogeology as tood on a vast,    plain very like ti of Africa today. to te deep. t    t, and never had been, any voloes inNebraska.

        today, te of Voorate Park, and it ylisors’ ter and museum, ful displays on tory of ter incorporates a lab ors    cologists ing bones.    alone in t ary in wured.

        t get a ors to Asate Park—it’s sligo sook me to t atop a ty-foot ravine where he had made his find.

        “It o look for bones,”    I    looking for bones. Iern Nebraska at time, and really just kindof poking around. If I    gone up t just    skull,I’d ed a roofedenclosure nearby, e. Some ther in a jumble.

        I asked     o    for bones. “ell, if you’re looking forbones, you really need exposed rock. t’s ology is done in , dry places.

        It’s not t t’s just t you ting them.

        In a setting like ture across t and unvarying prairie—“you    kno stuff out tto so start looking.”

        At first t tated as mual Geograpicle in 1981. “ticle called te a ‘Pompeii of preoriimals,’ ” old me, “e because just after t died suddenly at all. tropeodystrop you    if you    of abrasive as    of it because tt and crumbled itinto my     sligty. “Nasty stuff to o breat on,“because it’s very fi also quite s urer into an undrinkablegray sludge. It couldn’t    all.”

        tary ed t tence of so muebraska’s s    for a long time. Foralmost a tury to make    andAjax. But curiously no oo wonder whe ash came from.

        “I’m a little embarrassed to tell you,” Voor t I tabout it    tional Geograpo fess t I didn’t know. Nobody knew.”

        Voor samples to colleagues all over tern Uates asking if t it t ter a geologist named BillBonni toucold    t a place called Bruneau-Jarbidge in sout Ida tkilled t big enougo leave an ase deep almost a tern Nebraska. It turned out t uern Uates t spot, aclysmically every600,000 years or so. t su    over 600,000 years ago. t spot isstill t Yellooional Park.

        e knotle about    is fairly remarkable tot Ford    t tis moveabout on tion.

        “Strange as it may seem,” e Rid tribution of matterin terior of tter tand terior of th.”

        tance from to ter is 3,959 miles, w so very far.

        It ed t if you sunk a o ter and dropped a brito it, it ake only forty-five minutes for it to    ttom (t t point it    rat).

        Our otempts to pee to indeed. One or to a dept most mines o a quarter of a mile be    yet even e close.

        Until sligury ago, -informed stifids kerior    muc a iner kne you could digdoand t rod t    it. t named R. D. Oldemala, noticed t certain srated to a point deep an angle, as if tered some kind ofbarrier. From t ter a Croatianseismologist named Andrija Moudying grapiced a similar odd defle, but at a s and tely belole; tinuity, or Mo.

        e o get a vague idea of terior—t really    until 1936 did a Danisist named Inge Leudyingseismograp t o be solid and an outer o Oldected) tis t to be liquid and t of magism.

        At just about time t Leanding of terior by studying ts at Calteake parisoer and Beno Gutenberg, t o do    at once as Ric o do ereit fello al“tude Scale.”)ter scale ood by noists, ttle less so nos early days o Ri asked to seeed scale, t rary measure of tremblings based on surfacemeasurements. It rises expoially, so t a 7.3 quake is fifty times more poimes more pohquake.

        At least tically, t for ao t, a lo. t says not damage. A magnitude 7quake le—say, four    cause no surfacedamage at all, ation. Mucoo, depends on ture of tion, ty of aftersting of ted area. All t t fearsome quakes are not necessarily tforceful, ts for a lot.

        t eartion ered on Prince illiam Sound in Alaska in Marcer scale, or one in t of Cially logged at 8.6 magnitude but later revised upies(includiates Geological Survey) to a truly grand-scale 9.5. As you    al sce, particularly ing readings from remote locations. At all events, bot only caused al Sout also set offa giant tsunami t rolled six to more victims as far ahe Philippines.

        For pure, focused, devastation,    inteory    strud essentially so pieces—Lisbon, Pal, on All SaintsDay (November 1), 1755. Just before ten in ty ed at magnitude 9.0 and ses.

        t t ter rus of ty’s urnedin a y feet o tru.    last tion ceased, survivorsenjoyed just tes of calm before a sed sly less severe t. A t t all, sixty tually every building for miles reduced to rubble. timated 7.8 on ter scale andlasted less ty seds.

        Eartude 2.reater—t’s enougo give anyone nearby a pretty good jolt.

        Altend to cluster iain plaotably around t anyates, only Florida, eastern texas, and t seem—so far—to be almost entirely immune. Neude 6.reater in t tensive local damage and (I    attest) knog pictures from walls and childrenfrom beds as far away as Neshire.

        t on types of eartes meet, as in Californiaalong t. As tes pus eae or terval beter t-up pressure a. ticular okyo,    Uy College London, describesas “ty ing to die” (not a motto you ourism leaflets). tokyo standsoonic plates in a try already s seismistability. In 1995, as you y of Kobe, to t,ruck by a magnitude 7.2 quake, edat $99 billion. But t ively little—pared may a tokyo.

        tokyo    devastatiimes. Oember 1, 1923, just before noon, ty    Kantoquake—a more ten times more poime, tokyo , so traiy years. Eventually it is bound to snap. In 1923,tokyo ion of about today it is approacy million. Nobodycares to guess    die, but tential eic cost    asrillion.

        Even more unnerving, because tood and capable of anyime, are type of sraplate quakes. te boundaries, er deptend tate over muotorious suco    ted States er of 1811–12. ture started just after midnig by tiveness of animals before quakes is not an old ale, but is in fact ablis at all uood) and ty rupturing noise from deep o t    deep. A strong smell of sulfur filled ted for four miing effects to property. Among tnesses ist Joo be in ted out it knocked do least one at, “s i Coast harbors and .

        . . even collapsed scaffoldied around tol Building in ason, D.C.” OnJanuary 23 and February 4 furtude follo not surprisingly, since sug. tone could be under Co guess. And raplate rupturings? Somet know.

        By tists ly frustrated by tle tood ofterior t to try to do somet it. Specifically, t to drill tial crust oo to tinuity and to extract a piece of tle for examination at leisure. t if tand ture of tbegin to uaed, and to predict earts.

        t became kno iably, as t ty rous. to lo of Pacific O er off t of Mexid drill some 17,000 feet tively tal rock. Drilling froma sers is, in trying to drill a op tate Building using a strand of spagti.”

        Every attempt ended in failure. t trated    600 feet. ted s and s, gress killed t.

        Four years later, Soviet stists decided to try t onRussia’s Kola Peninsula,    to oa depteen kilometers. ted, but ts ent.    last teen years later, to adepters, or about 7.6 miles. Bearing in mind t t of ts only about 0.3 pert of t’s volume and t t cuteve, we    o erior.

        Iingly, even t, nearly everyt it was surprising.

        Seismic udies ists to predict, and pretty fidently, t ter sedimentary rock to a depters, folloe for t 2,300meters and basalt from t, tary layer deeper ted and tic layer    all. Moreover, ted, emperature at 10,000 meters of 180degrees tigrade, nearly ted level. Most surprising of all    t t depturated er—somet    been t possible.

        Because    see into to use otecly involvereading ravel terior. e also k about tlefrom e pipes,    fires, in effect, a onball of magma to t supersonic speeds. It is a totally random event. A kimberlite pipe could explode inyour backyard as you read to 120 milesdoe pipes bring up all kinds of t normally found on or ite, crystals of olivine, and—just occasionally, in about one pipein a s of carbon es up e ejecta, but most isvaporized or turns to grape. Only occasionally does a    s up at just tspeed and cool doo bee a diamond. It ive diamond mining city in t t    kno. Geologists kno someern Indiana t may be trulycolossal. Diamonds up to ty carats or more    scattered sites tt no one es, it may be buriedunder glacially deposited soil, like ter in Io Lakes.

        So    tle. Stists aregenerally agreed t ter crust, amantle of , viscous rock, a liquid outer core, and a solid inner core.

        1e kno ted by silicates, for t’s overall density. t be uff inside. e kno togee ic field some be a trated belt ofmetallic elements in a liquid state. t muc everyt—eract, o bet any time in ture—is a matter of at least some uainty, and generallyquite a lot of uainty.

        Even t of it , is a matter of some fairly stridee.

        Nearly all geology texts tell you t tial crust is to six miles t ty-five miles tis, and forty to sixty miles tain c ties ions. t beains, for instance, is only abouteen to ty-five miles to quid. (Some people tailed picture of terior, o 40 km (25 mi) is t. From 40 to 400 km (25 to 250 mi) is tle. From 400 to 650 km (250 to 400 mi) is a transition zole.

        From 650 to 2,700 km (400 to 1,700 mi) is tle. From 2,700 to 2,890 km (1,700 to 1,900 mi) is t;D" layer. From 2,890 to 5,150 km (1,900 to 3,200 mi) is ter core, and from 5,150 to 6,378 km (3,200 to3,967 mi) is the inner core.

        its crust are questions t divide geologists into t ly early in tory and t er. Strengtters. Rig of Yale proposed an early-burst t t of ing t agree    slybefore    at i a polemi an Australia cuating myto a report ih magazine in 1998.

        “ter man,” reported a colleague.

        t and part of ter maogetone”), s on top of a layer of softer rock called t strengt sucerms are irely satisfactory. to say t ts on top of ts adegree of easy buoyancy t isn’t quite rig is misleading to terials flo only in t glass is. It may not look it, but all tless drag of gravity. Remove a pane of really old glassfrom t iceably t ttom t top. t is t of “floalking about. t ten times faster tle.

        ts ocot just laterally as tes move across t upand doion.

        ve as a process    deduced by tric t von Rumford at teentury. Sixty years later an Englislysuggested t terients to move about,but t idea took a very long time to gain support.

        In about 1970,    urmoil    came as a siderable s it in t ists    decades figuring out tmospropospratosp about wind.”

        ion process goes ter of troversy ever since. Somesay it begins four refil    “ts of data, from t discipli ot be reciled.” Geocs say t certais ole, but must h.

        terials in tle must at least occasionally mix.

        Seismologists insist t to support suchesis.

        So all t    be said is t at some sligerminate point as er of Earto pure mantle. sidering t itats for 82 pert of t of its mass, tle doesn’tattract a great deal of attention, largely because t i Eartists andgeneral readers alike ism) or    to a dept a le sistspredominantly of a type of rooite, but ain. Acc to a Nature report, it seems not to be peridotite. More t know.

        Bele are ter one. Needless tosay, our uanding of ture of t, but stists    make somereasonable assumptions. t t ter of tly imes t to turn anyrock tory (among ot t retaining its . Alt is little more t is t t inover four billion years temperature at tly    t estimates range from someto 13,000°F—about as    as the Sun.

        ter core is in many ood, tt it is fluid and t it is t of magism. t forward by E. C.

        Bullard of Cambridge Uy in 1949 t t of t makes it, in effect, arical motor, creating tic field. tion is t ting fluids in t somes in wires.

        Exactly    it is felt pretty certain t it is ected s being liquid. Bodies t don’t ance—don’t ism.

        e kic field cime to time: during t o times as strong as no it reverses itselfevery 500,000 years or so on average, t average ability. t reversal    750,000 years ago. Sometimes it stays put formillions of years—37 million years appears to be t stretes it er as little as 20,000 years. Altoget 100 million years it self about t    est unansion in the geological sces.”

        e may be going tic field    in t tury alone. Any diminution in magism is likelyto be bad neism, apart from es to refrigerators and keeping ourpasses pointing t al role in keeping us alive. Space is full ofdangerous ic rays t in tic prote ear tatters. ic field is o ts. teract icles in tmospo createtohe auroras.

        A big part of terestingly enoug traditionally ttle effort to coordinate ’s going oninside. Acc to Ss and geops rarely go to tings or collaborate on the same problems.”

        Perter demonstrates our ie grasp of terior t out s up, and it ary reminder of tations of our uanding tion ofMount St. on in 1980.

        At t time, ty-eiged States    seen a volic eruption for oversixty-five years. t volologists called in to monitor and forecast St.

        ion, and t tur,    t all.

        St. arted its ominous rumblings on Margmagma, albeit in modest amounts, up to a imes a day, and being stantly sed to o be a safe distance of eigain’s rumblings gre. ourist attra for the world.

        Nes on t places to get a vieelevision creedlyfleo t, and people ain. Onone day, more ty copters and lig circled t. But as to develop into anytic, people greless, andt t going to bloer all.

        On April 19 tain began to bulge spicuously. Remarkably,no one in a position of responsibility sa trongly signaled a lateral blast. ts resolutely based t blo side t somet    a unity college in taa. ed out t St.    , as o be released dramatically and probablycatastrop part of team and ionsattracted little notice.

        e all kno 8:32 A.M. on a Sunday m, May 18, t and rock rusain slope at 150 miles an     landslide in ory andcarried enougerial to bury ttan to a dept. Amier, its flank severely . omibs, sing out a murderous    cloud at up to 650 miles anoo fast, clearly, for anyone nearby to outrace. Many people obe in safe areas, often far out of sigaken. Fifty-seven people y-toll    it een miles away.

        t person on t day e student named ion post 5.7 miles from tain, but interviee tion. aken by David Joon. Joon    to report ts later emporary.

        Eleven years later y-tists and journalists fatally caugp of supered asen rock—iount Unzen in Japan astrophically misread.

        Volologists may or may not be t stists in t making predis,but t question t in t realizing ions are.

        Less ter tastropley illiams of ty of Arizona, desded into tive volocalled Galeras in bia. Despite t years, only teenmembers of illiams’s party y s or otective gear. ted, killing six of tists, along ourists whers, including illiams himself.

        In araordinarily unself-critical book called Surviving Galeras, illiams said er ed t ant seismic signalsand be is to ser t, to apply to ts of 1993,” e. y of notiming    to do. I    I ake responsibility. But I do not feel guilty about t. tion.”

        But to return to ason. Mount St.    teen    of peak, and 230square miles of forest ated. Enougrees to build 150,000 s)    $2.7 billion. A giant n ofsmoke and aso a    of sixty t ien minutes. An airlinersome ty miles aed beied h rocks.

        y    minutes    after    t, aso rain doy of fifty t eig, turned day to nig into everyteors, aricalsc, s, blog filtration systems, and generally bringingto a . t s doy were closed.

        All te, just do    Yakima y’semergency broadcast system, o a during a crisis, did notgo on taff did not k.”

        For t off from ts airport closed, itsapproacogety received just five-eiger tion of Mount St.    in mind, please, as one blast would do.
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