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鈥渉e was just a great guy；鈥潯itzke replied without hesitation。 鈥渋f it hadn鈥檛 been for him； thewhole thing would never have gotten off the ground。 even with his support； it took two yearsto get it up and running。 drilling鈥檚 an expensive business鈥攁bout thirty…five dollars a footback then； more now； and we needed to go down three thousand feet。鈥�
鈥渟ometimes more than that；鈥潯nderson added。
鈥渟ometimes more than that；鈥潯itzke agreed。 鈥渁nd at several locations。 so you鈥檙e talking alot of money。 certainly more than our budget would allow。鈥�
so a collaboration was formed between the iowa geological survey and the u。s。
geological survey。
鈥渁t least we thought it was a collaboration；鈥潯aid anderson； producing a small painedsmile。
鈥渋t was a real learning curve for us；鈥潯itzke went on。 鈥渢here was actually quite a lot of badscience going on throughout the period鈥攑eople rushing in with results that didn鈥檛 alwaysstand up to scrutiny。鈥潯ne of those moments came at the annual meeting of the americangeophysical union in 1985； when glenn izett and c。 l。 pillmore of the u。s。 geologicalsurvey announced that the manson crater was of the right age to have been involved with thedinosaurs鈥櫋xtinction。 the declaration attracted a good deal of press attention but wasunfortunately premature。 a more careful examination of the data revealed that manson wasnot only too small； but also nine million years too early。
the first anderson or witzke learned of this setback to their careers was when they arrivedat a conference in south dakota and found people ing up to them with sympathetic looksand saying： 鈥渨e hear you lost your crater。鈥潯t was the first they knew that izett and the otherusgs scientists had just announced refined figures revealing that manson couldn鈥檛 after allhave been the extinction crater。
鈥渋t was pretty stunning；鈥潯ecalls anderson。 鈥渋 mean； we had this thing that was reallyimportant and then suddenly we didn鈥檛 have it anymore。 but even worse was the realizationthat the people we thought we鈥檇 been collaborating with hadn鈥檛 bothered 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 catastro