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ed by volcanic action even while conceding in a newspaper interviewthat he had no actual evidence of it。 as late as 1988 more than half of all americanpaleontologists contacted in a survey continued to believe that the extinction of the dinosaurswas in no way related to an asteroid or etary impact。
the one thing that would most obviously support the alvarezes鈥櫋heory was the one thingthey didn鈥檛 have鈥攁n impact site。 enter eugene shoemaker。 shoemaker had an iowaconnection鈥攈is daughter…in…law taught at the university of iowa鈥攁nd he was familiar withthe manson crater from his own studies。 thanks to him； all eyes now turned to iowa。
geology is a profession that varies from place to place。 in iowa； a state that is flat andstratigraphically uneventful； it tends to be paratively serene。 there are no alpine peaks orgrinding glaciers； no great deposits of oil or precious metals； not a hint of a pyroclastic flow。
if you are a geologist employed by the state of iowa； a big part of the work you do is toevaluate manure management plans； which all the state鈥檚 鈥渁nimal confinement operators鈥濃�攈og farmers to the rest of us鈥攁re required to file periodically。 there are fifteen million hogsin iowa； so a lot of manure to manage。 i鈥檓 not mocking this at all鈥攊t鈥檚 vital and enlightenedwork； it keeps iowa鈥檚 water clean鈥攂ut with the best will in the world it鈥檚 not exactly dodginglava bombs on mount pinatubo or scrabbling over crevasses on the greenland ice sheet insearch of ancient life…bearing quartzes。 so we may well imagine the flutter of excitement thatswept through the iowa department of natural resources when in the mid…1980s the world鈥檚geological attention focused on manson and its crater。
trowbridge hall in iowa city is a turn…of…the…century pile of red brick that houses theuniversity of iowa鈥檚 earth sciences department and鈥攚ay up in a kind of garret鈥攖hegeologists of the iowa department of natural resources。 no one now can remember quitewhen； still less why； the state geologists were placed in an academic facility； but you get theimpression that the space was conceded grudgingly； for the offices are cramped and low…ceilinged and not very accessible。 when being shown the way； you half expect to be taken outonto a roof ledge and helped in through a window。
ray anderson and brian witzke spend their working lives up here amid disordered heapsof papers； journals； furled charts； and hefty specimen stones。 （geologists are never at a lossfor paperweights。） it鈥檚 the kind of space where if you want to find anything鈥攁n extra chair； acoffee cup； a ringing telephone鈥攜ou have to move stacks of documents around。
鈥渟uddenly we were at the center of things；鈥潯nderson told me； gleaming at the memory ofit； when i met him and witzke in their offices on a dismal； rainy morning in june。 鈥渋t was awonderful time。鈥�
i asked them about gene shoemaker； a man who seems to have been universally revered。
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