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d 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 ashfall fossil beds state park； and it has astyl