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nts not normally much found on earth。 among these is the element iridium；which is a thousand times more abundant in space than in the earth’s crust （because； it isthought； most of the iridium on earth sank to the core when the planet was young）。
alvarez knew that a colleague of his at the lawrence berkeley laboratory in california；frank asaro； had developed a technique for measuring very precisely the chemicalposition of clays using a process called neutron activation analysis。 this involvedbombarding samples with neutrons in a small nuclear reactor and carefully counting thegamma rays that were emitted； it was extremely finicky work。 previously asaro had used thetechnique to analyze pieces of pottery； but alvarez reasoned that if they measured the amountof one of the exotic elements in his son’s soil samples and pared that with its annual rateof deposition； they would know how long it had taken the samples to form。 on an octoberafternoon in 1977； luis and walter alvarez dropped in on asaro and asked him if he wouldrun the necessary tests for them。
it was really quite a presumptuous request。 they were asking asaro to devote months tomaking the most painstaking measurements of geological samples merely to confirm whatseemed entirely self…evident to begin with—that the thin layer of clay had been formed asquickly as its thinness suggested。 certainly no one expected his survey to yield any dramaticbreakthroughs。
“well； they were very charming； very persuasive；” asaro recalled in an interview in 2002。
“and 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。” he consulted his notes from theperiod。 “on 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。”
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—far beyond anything they might have predicted。 over the following monthsasaro and his colleague helen michel worked up to thirty hours at a stretch （“once youstarted you couldn’t stop；” asaro explained） analyzing samples； always with the same results。
tests on other samples—from denmark； spain； france； new zealand； antarctica—showedthat 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—plausible to them； at any rate—was 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’s 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 （“it’s five miles wide 。 。 。 it’sing at 30；000 m。p。h。—and there’s no place to hide！”） starring 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’t have e as a shock。
but it did。 it was received everywhere； but particularly in the paleontological munity；as an outrageous heresy。
“well； you have to remember；” asaro recalls； “that 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’s not terribly surprising that they didn’t embrace itimmediately。” as luis alvarez joked： “we were caught practicing geology without alicense。”
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； “against their scientific religion。”
nor did it help that luis alvarez was openly contemptuous of paleontologists and theircontributions to scientific knowledge。 “they’re really not very good scientists。 they’re morelike stamp collectors；” he 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—for instance； that they were generated by prolonged volcanic eruptions inindia called the deccan traps—and 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 w