ed to share with us theirnew findings。鈥�
鈥渨hy not？鈥�
he shrugged。 鈥渨ho knows？ anyway； it was a pretty good insight into how unattractivescience can get when you鈥檙e playing at a certain level。鈥�
the search moved elsewhere。 by chance in 1990 one of the searchers； alan hildebrand ofthe university of arizona； met a reporter from the houston chronicle who happened to knowabout a large； unexplained ring formation； 120 miles wide and 30 miles deep； under mexico鈥檚yucat谩n peninsula at chicxulub； near the city of progreso； about 600 miles due south of neworleans。 the formation had been found by pemex； the mexican oil pany； in 1952鈥攖heyear； coincidentally； that gene shoemaker first visited meteor crater in arizona鈥攂ut thepany鈥檚 geologists had concluded that it was volcanic； in line with the thinking of the day。
hildebrand traveled to the site and decided fairly swiftly that they had their crater。 by early1991 it had been established to nearly everyone鈥檚 satisfaction that chicxulub was the impactsite。
still； many people didn鈥檛 quite grasp what an impact could do。 as stephen jay gouldrecalled in one of his essays： 鈥渋 remember harboring some strong initial doubts about theefficacy of such an event 。 。 。 ＇w＇hy should an object only six miles across wreak such havocupon a planet with a diameter of eight thousand miles？鈥�
conveniently a natural test of the theory arose when the shoemakers and levy discoveredet shoemaker…levy 9； which they soon realized was headed for jupiter。 for the first time；humans would be able to witness a cosmic collision鈥攁nd witness it very well thanks to thenew hubble space telescope。 most astronomers； according to curtis peebles； expected little；particularly as the et was not a coherent sphere but a string of twenty…one fragments。 鈥渕ysense；鈥潯rote one； 鈥渋s that jupiter will swallow these ets up without so much as a burp。鈥�
one week before the impact； nature ran an article； 鈥渢he big fizzle is ing；鈥潯redictingthat the impact would constitute nothing more than a meteor shower。
the impacts began on july 16； 1994； went on for a week and were bigger by far thananyone鈥攚ith the possible exception of gene shoemaker鈥攅xpected。 one fragment； knownas nucleus g； struck with the force of about six million megatons鈥攕eventy…five times morethan all the nuclear weaponry in existence。 nucleus g was only about the size of a smallmountain； but it created wounds in the jovian surface the size of earth。 it was the final blowfor critics of the alvarez theory。
luis alvarez never knew of the discovery of the chicxulub crater or of the shoemaker…levy et； as he died in 1988。 shoemaker also died early。 on the third anniversary of theshoemaker…levy impact； he and his wife were in the australian outback； where they wentevery year to search for impact sites。 on a dirt track in the tanami desert鈥攏ormally one ofthe emptiest places on earth鈥攖hey came over a slight rise just as another vehicle wasapproaching。 shoemaker was killed instantly； his wife injured。 part of his ashes were sent tothe moon aboard the lunar prospector spacecraft。 the rest were scattered around meteorcrater。
anderson and witzke no longer had the crater that killed the dinosaurs； 鈥渂ut we still hadthe largest and most perfectly preserved impact crater in the mainland united states；鈥�
anderson said。 （a little verbal dexterity is required to keep manson鈥檚 superlative status。 othercraters are larger鈥攏otably； chesapeake bay； which was recognized as an impact site in1994鈥攂ut they are either offshore or deformed。） 鈥渃hicxulub is buried under two to threekilometers of limestone and mostly offshore； which makes it difficult to study；鈥潯ndersonwent on； 鈥渨hile manson is really quite accessible。 it鈥檚 because it is buried that it is actuallyparatively pristine。鈥�
i asked them how much warning we would receive if a similar hunk of rock was ingtoward us today。
鈥渙h； probably none；鈥潯aid anderson breezily。 鈥渋t wouldn鈥檛 be visible to the naked eye untilit warmed up； and that wouldn鈥檛 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 would