peared abruptly from the fossil record at the iridium boundary。 one of the most vigorous opponents was charles officer of dartmouth college。 he insisted that theiridium had been deposited 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’ theory was the one thingthey didn’t have—an impact site。 enter eugene shoemaker。 shoemaker had an iowaconnection—his daughter…in…law taught at the university of iowa—and 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’s “animal confinement operators”—hog farmers to the rest of us—are required to file periodically。 there are fifteen million hogsin iowa； so a lot of manure to manage。 i’m not mocking this at all—it’s vital and enlightenedwork； it keeps iowa’s water clean—but with the best will in the world it’s 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’sgeological 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’s earth sciences department and—way up in a kind of garret—thegeologists 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’s the kind of space where if you want to find anything—an extra chair； acoffee cup； a ringing telephone—you have to move stacks of documents around。
“suddenly we were at the center of things；” anderson told me； gleaming at the memory ofit； when i met him and witzke in their offices on a dismal； rainy morning in june。 “it was awonderful time。”
i asked them about gene shoemaker； a man who seems to have been universally revered。
“he was just a great guy；” witzke replied without hesitation。 “if it hadn’t 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’s an expensive business—about thirty…five dollars a footback then； more now； and we needed to go down three thousand feet。”
“sometimes more than that；” anderson added。
“sometimes more than that；” witzke agreed。 “and at several locations。 so you’re talking alot of money。 certainly more than our budget would allow。”
so a collaboration was formed between the iowa geological survey and the u。s。
geological survey。
“at least we thought it was a collaboration；” said anderson； producing a small painedsmile。
“it was a real learning curve for us；” witzke went on。 “there was actually quite a lot of badscience going on throughout the period—people rushing in with results that didn’t alwaysstand up to scrutiny。” one 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’ extinction。 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： “we hear you lost your crater。” it was the first they knew that izett and the otherusgs scientists had just announced refined figures revealing that manson couldn’t after allhave been the extinction crater。
“it was pretty stunning；” recalls anderson。 “i mean； we had this thing that was reallyimportant and then suddenly we didn’t have it anymore。 but even worse was the realizationthat the people we thought we’d been collaborating with hadn’t bothered to share with us theirnew findings。”
“why not？”
he shrugged。 “who knows？ anyway； it was a pretty good insight into how unattractivescience can get when you’re playing at a certain level。”
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’syucatán 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—theyear； coincidentally； that gene shoemaker first visited meteor crater in arizona—but thepany’s 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’s satisfaction that chicxulub was the impactsite。
still； many people didn’t quite grasp what an impact could do。 as stephen jay gouldrecalled in one of his essays： “i 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？”
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—and 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。 “mysense；” wrote one； “is that jupiter will swallow these ets up without so much as a burp。”
one week before the impact； nature ran an article； “the big fizzle is ing；” predictingthat 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—with the possible exception of gene shoemaker—expected。 one fragment； knownas nucleus g； struck with the force of about six million megatons—seventy…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—normally one ofthe emptiest places on earth—they 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； “but we still hadthe largest and most perfectly preserved impact crater in the mainland united states；”
anderson said。 （a little verbal dexterity is required to keep manson’s superlative status。 othercraters are larger—notably； chesapeake bay； which was recognized as an impact site in1994—but they are either offshore or deformed。） “chicxulub is buried under two to threekilometers of limestone and mostly offshore； which makes it difficult to study；” andersonwent on； “while manson is really quite accessible。 it’s because it is buried that it is actuallyparatively pristine。”
i asked them how much warning we would receive if a similar hunk of rock was ingtoward us today。
“oh； probably none；” said anderson breezily。 “it wouldn’t be visible to the naked eye untilit warmed up； and that wouldn’t happen until i