A short history of nearly everything - Bill Bryson [96]
It was really quite a presumptuous request. They were asking Asaro to devote months to making the most painstaking measurements of geological samples merely to confirm what seemed entirely self-evident to begin with—that the thin layer of clay had been formed as quickly as its thinness suggested. Certainly no one expected his survey to yield any dramatic breakthroughs.
“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 other work on, so it was eight months before I could get to it.” He consulted his notes from the period. “On June 21, 1978, at 1:45 p.m., we put a sample in the detector. It ran for 224 minutes and we could see we were getting interesting results, so we stopped it and had a look.”
The results were so unexpected, in fact, that the three scientists at first thought they had to be wrong. The amount of iridium in the Alvarez sample was more than three hundred times normal levels—far beyond anything they might have predicted. Over the following months Asaro and his colleague Helen Michel worked up to thirty hours at a stretch (“Once you started you couldn't stop,” Asaro explained) analyzing samples, always with the same results. Tests on other samples—from Denmark, Spain, France, New Zealand, Antarctica—showed that the iridium deposit was worldwide and greatly elevated everywhere, sometimes by as much as five hundred times normal levels. Clearly something big and abrupt, and probably cataclysmic, 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 comet.
The idea that the Earth might be subjected to devastating impacts from time to time was not quite as new as it is now sometimes presented. As far back as 1942, a Northwestern University astrophysicist named Ralph B. Baldwin had suggested such a possibility in an article in Popular Astronomy magazine. (He published the article there because no academic publisher was prepared to run it.) And at least two well-known scientists, the astronomer Ernst Öpik and the chemist and Nobel laureate Harold Urey, had also voiced support for the notion at various times. Even among paleontologists it was not unknown. In 1956 a professor at Oregon State University, M. W. de Laubenfels, writing in the Journal of Paleontology, had actually anticipated the Alvarez theory by suggesting that the dinosaurs may have been dealt a death blow by an impact from space, and in 1970 the president of the American Paleontological Society, Dewey J. McLaren, proposed at the group's annual conference the possibility that an extraterrestrial impact may have been the cause of an earlier event known as the Frasnian extinction.
As if to underline just how un-novel the idea had become by this time, in 1979 a Hollywood studio actually produced a movie called Meteor (“It's five miles wide . . . It's coming at 30,000 m.p.h.—and there's no place to hide!”) starring Henry Fonda, Natalie Wood, Karl Malden, and a very large rock.
So when, in the first week of 1980, at a meeting of the American Association for the Advancement of Science, the Alvarezes announced their belief that the dinosaur extinction had not taken place over millions of