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happen until it hit the atmosphere； which would be about onesecond before it hit the earth。 you鈥檙e talking about something moving many tens of timesfaster than the fastest bullet。 unless it had been seen by someone with a telescope； and that鈥檚by no means a certainty； it would take us pletely by surprise。鈥�
how hard an impactor hits depends on a lot of variables鈥攁ngle 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鈥攏one of which we can know so many millions of yearsafter the fact。 but what scientists can do鈥攁nd anderson and witzke have done鈥攊s 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鈥攐r； more chillingly； would be like if ithappened now。
an asteroid or et traveling at cosmic velocities would enter the earth鈥檚 atmosphere atsuch a speed that the air beneath it couldn鈥檛 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鈥檚 path鈥攑eople； houses； factories； cars鈥攚ould crinkle and vanish like cellophane in aflame。
one second after entering the atmosphere； the meteorite would slam into the earth鈥檚surface； 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鈥檛 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鈥攖he brightest ever seen by human eyes鈥攆ollowed 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鈥攖he whole of the midwest； inshort鈥攏early 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鈥檚 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 鈥渟electing a slow death over aquick one。 the death toll would be very little affected by any plausible relocation effort； sinceearth鈥檚 ability to support life would be universally diminished。鈥�
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鈥檚 climate for about ten thousand years。
this was actually used as evidence to support the notion that the extinction of dinosaurs wasswift and emphatic鈥攁nd 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鈥檚 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鈥檛 the oomph to escape earth鈥檚 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鈥攂ut with the differencethat now the rocks would be intensely radioactive。 tom gehrels； an asteroid hunter at theuniversity of arizona； thinks that even a year鈥檚 warning would probably be insufficient totake appropriate action。 the greater likelihood； however； is that we wouldn鈥檛 see any object鈥攅ven a et鈥攗ntil 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鈥檛know until nearly the end鈥攖he last couple of weeks anyway鈥攚hether collision was certain。
for most of the time of the object鈥檚 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。
鈥渟o how often does something like the manson impact happen？鈥潯 asked anderson andwitzke before leaving。
鈥渙h； about once every million years on average；鈥潯aid witzke。
鈥渁nd remember；鈥潯dded anderson； 鈥渢his was a relatively minor event。 do you know howmany extinctions were associated with the manson impact？鈥�
鈥渘o idea；鈥潯 replied。
鈥渘one；鈥潯e said； with a strange air of satisfaction。 鈥渘ot one。鈥�
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鈥檛 actually necessary tolook to space for petrifying danger。 as we are about to see； earth can provide plenty of dangerof its own。
14 THE FIRE BELOW
灏忚txt澶╁爞
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鈥攔hinoceroses； 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鈥檚 discovery is called ashfall fossil beds state park； and it has astylish new visitors鈥櫋