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ed entirely self…evident to begin with鈥攖hat the thin layer of clay had been formed asquickly as its thinness suggested。 certainly no one expected his survey to yield any dramaticbreakthroughs。
鈥渨ell； they were very charming； very persuasive；鈥潯saro recalled in an interview in 2002。
鈥渁nd it seemed an interesting challenge； so i agreed to try。 unfortunately； i had a lot of otherwork on； so it was eight months before i could get to it。鈥潯e consulted his notes from theperiod。 鈥渙n june 21； 1978； at 1：45 p。m。； we put a sample in the detector。 it ran for 224minutes and we could see we were getting interesting results； so we stopped it and had alook。鈥�
the results were so unexpected； in fact； that the three scientists at first thought they had tobe wrong。 the amount of iridium in the alvarez sample was more than three hundred timesnormal levels鈥攆ar beyond anything they might have predicted。 over the following monthsasaro and his colleague helen michel worked up to thirty hours at a stretch （鈥渙nce youstarted you couldn鈥檛 stop；鈥潯saro explained） analyzing samples； always with the same results。
tests on other samples鈥攆rom denmark； spain； france； new zealand； antarctica鈥攕howedthat the iridium deposit was worldwide and greatly elevated everywhere； sometimes by asmuch as five hundred times normal levels。 clearly something big and abrupt； and probablycataclysmic； had produced this arresting spike。
after much thought； the alvarezes concluded that the most plausible explanation鈥攑lausible to them； at any rate鈥攚as that the earth had been struck by an asteroid or et。
the idea that the earth might be subjected to devastating impacts from time to time was notquite as new as it is now sometimes presented。 as far back as 1942； a northwesternuniversity astrophysicist named ralph b。 baldwin had suggested such a possibility in anarticle in popular astronomy magazine。 （he published the article there because no academicpublisher was prepared to run it。） and at least two well…known scientists； the astronomerernst ？pik and the chemist and nobel laureate harold urey； had also voiced support for thenotion at various times。 even among paleontologists it was not unknown。 in 1956 a professorat oregon state university； m。 w。 de laubenfels； writing in the journal of paleontology； hadactually anticipated the alvarez theory by suggesting that the dinosaurs may have been dealt adeath blow by an impact from space； and in 1970 the president of the americanpaleontological society； dewey j。 mclaren； proposed at the group鈥檚 annual conference thepossibility that an extraterrestrial impact may have been the cause of an earlier event knownas the frasnian extinction。
as if to underline just how un…novel the idea had bee by this time； in 1979 ahollywood studio actually produced a movie called meteor （鈥渋t鈥檚 five miles wide 。 。 。 it鈥檚ing at 30；000 m。p。h。鈥攁nd there鈥檚 no place to hide！鈥潱tarring henry fonda； nataliewood； karl malden； and a very large rock。
so when； in the first week of 1980； at a meeting of the american association for theadvancement of science； the alvarezes announced their belief that the dinosaur extinctionhad not taken place over millions of years as part of some slow inexorable process； butsuddenly in a single explosive event； it shouldn鈥檛 have e as a shock。
but it did。 it was received everywhere； but particularly in the paleontological munity；as an outrageous heresy。
鈥渨ell； you have to remember；鈥潯saro recalls； 鈥渢hat we were amateurs in this field。 walterwas a geologist specializing in paleomagnetism； luis was a physicist and i was a nuclearchemist。 and now here we were telling paleontologists that we had solved a problem that hadeluded them for over a century。 it鈥檚 not terribly surprising that they didn鈥檛 embrace itimmediately。鈥潯s luis alvarez joked： 鈥渨e were caught practicing geology without alicense。鈥�
but there was also something much deeper and more fundamentally abhorrent in the impacttheory。 the belief that terrestrial processes were gradual had been elemental in natural historysince the time of lyell。 by the 1980s； catastrophism had been out of fashion for so long that ithad bee literally unthinkable。 for most geologists the idea of a devastating impact was； aseugene shoemaker noted； 鈥渁gainst their scientific religion。鈥�
nor did it help that luis alvarez was openly contemptuous of paleontologists and theircontributions to scientific knowledge。 鈥渢hey鈥檙e really not very good scientists。 they鈥檙e morelike stamp collectors；鈥潯e wrote in the new york times in an article that stings yet。
opponents of the alvarez theory produced any number of alternative explanations for theiridium deposits鈥攆or instance； that they were generated by prolonged volcanic eruptions inindia called the deccan traps鈥攁nd above all insisted that there was no proof that thedinosaurs disappeared 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