Recently, on a National Public Radio retrospective on American life a quarter-century ago, a commentator remarked that 1963 was one of the last years when we knew that the dinosaurs died out “because they were stupid, just plain too stupid,” and not due to some exotic mechanism. In 1989, catastrophic causes still reign supreme. Yet, in the public's mind, the controversy has not yet been settled: was it an asteroid, explosive volcanism, or a comet shower? Technical debates have raged since the late Luis Alvarez, his son Walter, and their Berkeley coworkers distributed preprints nearly a decade ago of their seminal paper [Alvarez et al., 1980] on the extraterrestrial cause for mass extinctions at the end of the Cretaceous Period. A recent conference, Global Catastrophes in Earth History, has shown that the debate is now mainly over. The meeting was held October 20–22, 1988, at Snowbird, Utah, and hereafter I refer to it as the “Snowbird II meeting.”
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