A Short History of Nearly Everything- 第42部分

“oh；　probably　none；”　said　anderson　breezily。　“it　wouldn’t　be　visible　to　the　naked　eye　untilit　warmed　up；　and　that　wouldn’t　happen　until　it　hit　the　atmosphere；　which　would　be　about　onesecond　before　it　hit　the　earth。　you’re　talking　about　something　moving　many　tens　of　timesfaster　than　the　fastest　bullet。　unless　it　had　been　seen　by　someone　with　a　telescope；　and　that’sby　no　means　a　certainty；　it　would　take　us　pletely　by　surprise。”

how　hard　an　impactor　hits　depends　on　a　lot　of　variables—angle　of　entry；　velocity　andtrajectory；　whether　the　collision　is　head…on　or　from　the　side；　and　the　mass　and　density　of　theimpacting　object；　among　much　else—none　of　which　we　can　know　so　many　millions　of　yearsafter　the　fact。　but　what　scientists　can　do—and　anderson　and　witzke　have　done—is　measurethe　impact　site　and　calculate　the　amount　of　energy　released。　from　that　they　can　work　outplausible　scenarios　of　what　it　must　have　been　like—or；　more　chillingly；　would　be　like　if　ithappened　now。

an　asteroid　or　et　traveling　at　cosmic　velocities　would　enter　the　earth’s　atmosphere　atsuch　a　speed　that　the　air　beneath　it　couldn’t　get　out　of　the　way　and　would　be　pressed；　as　ina　bicycle　pump。　as　anyone　who　has　used　such　a　pump　knows；　pressed　air　grows　swiftlyhot；　and　the　temperature　below　it　would　rise　to　some　60；000　kelvin；　or　ten　times　the　surfacetemperature　of　the　sun。　in　this　instant　of　its　arrival　in　our　atmosphere；　everything　in　themeteor’s　path—people；　houses；　factories；　cars—would　crinkle　and　vanish　like　cellophane　in　aflame。

one　second　after　entering　the　atmosphere；　the　meteorite　would　slam　into　the　earth’ssurface；　where　the　people　of　manson　had　a　moment　before　been　going　about　their　business。

the　meteorite　itself　would　vaporize　instantly；　but　the　blast　would　blow　out　a　thousand　cubickilometers　of　rock；　earth；　and　superheated　gases。　every　living　thing　within　150　miles　thathadn’t　been　killed　by　the　heat　of　entry　would　now　be　killed　by　the　blast。　radiating　outward　atalmost　the　speed　of　light　would　be　the　initial　shock　wave；　sweeping　everything　before　it。

for　those　outside　the　zone　of　immediate　devastation；　the　first　inkling　of　catastrophe　wouldbe　a　flash　of　blinding　light—the　brightest　ever　seen　by　human　eyes—followed　an　instant　to　aminute　or　two　later　by　an　apocalyptic　sight　of　unimaginable　grandeur：　a　roiling　wall　ofdarkness　reaching　high　into　the　heavens；　filling　an　entire　field　of　view　and　traveling　atthousands　of　miles　an　hour。　its　approach　would　be　eerily　silent　since　it　would　be　moving　farbeyond　the　speed　of　sound。　anyone　in　a　tall　building　in　omaha　or　des　moines；　say；　whochanced　to　look　in　the　right　direction　would　see　a　bewildering　veil　of　turmoil　followed　byinstantaneous　oblivion。

within　minutes；　over　an　area　stretching　from　denver　to　detroit　and　enpassing　what　hadonce　been　chicago；　st。　louis；　kansas　city；　the　twin　cities—the　whole　of　the　midwest；　inshort—nearly　every　standing　thing　would　be　flattened　or　on　fire；　and　nearly　every　living　thingwould　be　dead。　people　up　to　a　thousand　miles　away　would　be　knocked　off　their　feet　and　slicedor　clobbered　by　a　blizzard　of　flying　projectiles。　beyond　a　thousand　miles　the　devastation　fromthe　blast　would　gradually　diminish。

but　that’s　just　the　initial　shockwave。　no　one　can　do　more　than　guess　what　the　associateddamage　would　be；　other　than　that　it　would　be　brisk　and　global。　the　impact　would　almostcertainly　set　off　a　chain　of　devastating　earthquakes。　volcanoes　across　the　globe　would　beginto　rumble　and　spew。　tsunamis　would　rise　up　and　head　devastatingly　for　distant　shores。　withinan　hour；　a　cloud　of　blackness　would　cover　the　planet；　and　burning　rock　and　other　debriswould　be　pelting　down　everywhere；　setting　much　of　the　planet　ablaze。　it　has　been　estimatedthat　at　least　a　billion　and　a　half　people　would　be　dead　by　the　end　of　the　first　day。　the　massivedisturbances　to　the　ionosphere　would　knock　out　munications　systems　everywhere；　sosurvivors　would　have　no　idea　what　was　happening　elsewhere　or　where　to　turn。　it　would　hardlymatter。　as　one　mentator　has　put　it；　fleeing　would　mean　“selecting　a　slow　death　over　aquick　one。　the　death　toll　would　be　very　little　affected　by　any　plausible　relocation　effort；　sinceearth’s　ability　to　support　life　would　be　universally　diminished。”

the　amount　of　soot　and　floating　ash　from　the　impact　and　following　fires　would　blot　out　thesun；　certainly　for　months；　possibly　for　years；　disrupting　growing　cycles。　in　2001　researchers　atthe　california　institute　of　technology　analyzed　helium　isotopes　from　sediments　left　from　thelater　kt　impact　and　concluded　that　it　affected　earth’s　climate　for　about　ten　thousand　years。

this　was　actually　used　as　evidence　to　support　the　notion　that　the　extinction　of　dinosaurs　wasswift　and　emphatic—and　so　it　was　in　geological　terms。　we　can　only　guess　how　well；　orwhether；　humanity　would　cope　with　such　an　event。

and　in　all　likelihood；　remember；　this　would　e　without　warning；　out　of　a　clear　sky。

but　let’s　assume　we　did　see　the　object　ing。　what　would　we　do？　everyone　assumes　wewould　send　up　a　nuclear　warhead　and　blast　it　to　smithereens。　the　idea　has　some　problems；however。　first；　as　john　s。　lewis　notes；　our　missiles　are　not　designed　for　space　work。　theyhaven’t　the　oomph　to　escape　earth’s　gravity　and；　even　if　they　did；　there　are　no　mechanisms　toguide　them　across　tens　of　millions　of　miles　of　space。　still　less　could　we　send　up　a　shipload　ofspace　cowboys　to　do　the　job　for　us；　as　in　the　movie　armageddon；　we　no　longer　possess　arocket　powerful　enough　to　send　humans　even　as　far　as　the　moon。　the　last　rocket　that　could；saturn　5；　was　retired　years　ago　and　has　never　been　replaced。　nor　could　we　quickly　build　anew　one　because；　amazingly；　the　plans　for　saturn　launchers　were　destroyed　as　part　of　anasa　housecleaning　exercise。

even　if　we　did　manage　somehow　to　get　a　warhead　to　the　asteroid　and　blasted　it　to　pieces；the　chances　are　that　we　would　simply　turn　it　into　a　string　of　rocks　that　would　slam　into　us　oneafter　the　other　in　the　manner　of　et　shoemaker…levy　on　jupiter—but　with　the　differencethat　now　the　rocks　would　be　intensely　radioactive。　tom　gehrels；　an　asteroid　hunter　at　theuniversity　of　arizona；　thinks　that　even　a　year’s　warning　would　probably　be　insufficient　totake　appropriate　action。　the　greater　likelihood；　however；　is　that　we　wouldn’t　see　any　object—even　a　et—until　it　was　about　six　months　away；　which　would　be　much　too　late。

shoemaker…levy　9　had　been　orbiting　jupiter　in　a　fairly　conspicuous　manner　since　1929；　but　ittook　over　half　a　century　before　anyone　noticed。

interestingly；　because　these　things　are　so　difficult　to　pute　and　must　incorporate　such　asignificant　margin　of　error；　even　if　we　knew　an　object　was　heading　our　way　we　wouldn’tknow　until　nearly　the　end—the　last　couple　of　weeks　anyway—whether　collision　was　certain。

for　most　of　the　time　of　the　object’s　approach　we　would　exist　in　a　kind　of　cone　of　uncertainty。

it　would　certainly　be　the　most　interesting　few　months　in　the　history　of　the　world。　and　imaginethe　party　if　it　passed　safely。

“so　how　often　does　something　like　the　manson　impact　happen？”　i　asked　anderson　andwitzke　before　leaving。

“oh；　about　once　every　million　years　on　average；”　said　witzke。

“and　remember；”　added　anderson；　“this　was　a　relatively　minor　event。　do　you　know　howmany　extinctions　were　associated　with　the　manson　impact？”

“no　idea；”　i　replied。

“none；”　he　said；　with　a　strange　air　of　satisfaction。　“not　one。”

of　course；　witzke　and　anderson　added　hastily　and　more　or　less　in　unison；　there　wouldhave　been　terrible　devastation　across　much　of　the　earth；　as　just　described；　and　pleteannihilation　for　hundreds　of　miles　around　ground　zero。　but　life　is　hardy；　and　when　the　smokecleared　there　were　enough　lucky　survivors　from　every　species　that　none　permanentlyperished。

the　good　news；　it　appears；　is　that　it　takes　an　awful　lot　to　extinguish　a　species。　the　badnews　is　that　the　good　news　can　never　be　counted　on。　worse　still；　it　isn’t　actually　necessary　tolook　to　space　for　petrifying　danger。　as　we　are　about　to　see；　earth　can　provide　plenty　of　dangerof　its　own。

。。！



14THE　FIRE　BELOW

　生
in　the　summer　of　1971；　a　young　geologist　named　mike　voorhies　was　scouting　around　onsome　grassy　farmland　in　eastern　nebraska；　not　far　from　the　little　town　of　orchard；　where　hehad　grown　up。　passing　through　a　steep…sided　gully；　he　spotted　a　curious　glint　in　the　brushabove　and　clambered　up　to　have　a　look。　what　he　had　seen　was　the　perfectly　preserved　skull　ofa　young　rhinoceros；　which　had　been　washed　out　by　recent　heavy　rains。

a　few　yards　beyond；　it　turned　out；　was　one　of　the　most　extraordinary　fossil　beds　everdiscovered　in　north　america；　a　dried…up　water　hole　that　had　served　as　a　mass　grave　for　scoresof　animals—rhinoceroses；　zebra…like　horses；　saber…toothed　deer；　camels；　turtles。　all　had　diedfrom　some　mysterious　cataclysm　just　under　twelve　million　years　ago　in　the　time　known　togeology　as　the　miocene。　in　those　days　nebraska　stood　on　a　vast；　hot　plain　very　like　theserengeti　of　africa　today。　the　animals　had　been　found　buried　under　volcanic　ash　up　to　tenfeet　deep。　the　puzzle　of　it　was　that　there　were　not；　and　never　had　been；　any　volcanoes　innebraska。

today；　the　site　of　voorhies’s　discovery　is　called　ashf