to be confused with “catastrophes.” The same year that the Alvarezes
published their paper in Science, George Gaylord Simpson, at the time
probably the world’s most influential paleontologist, wrote that the
“turnover” at the end of the Cretaceous should be regarded as part of “a
long and essentially continuous process.”
In the context of “hard-core uniformitarianism,” the impact
hypothesis was worse than wrong. The Alvarezes were claiming to
explain an event that hadn’t happened—one that couldn’t have happened.
It was like peddling patent medicine for a fictitious illness. A few years
after father and son published their hypothesis, an informal survey was
conducted at a meeting of the Society of Vertebrate Paleontology. A
majority of those surveyed said they thought some sort of cosmic
collision might have taken place. But only one in twenty thought it had
anything to do with the extinction of the dinosaurs. One paleontologist at
the meeting labeled the Alvarez hypothesis “codswallop.”
MEANWHILE, evidence for the hypothesis continued to accumulate.
The first independent corroboration came in the form of tiny grains of
rock known as “shocked quartz.” Under high magnification, shocked
quartz exhibits what look like scratch marks, the result of bursts of high
pressure that deform the crystal structure. Shocked quartz was first
noted at nuclear test sites and subsequently found in the immediate
vicinity of impact craters. In 1984, grains of shocked quartz were
discovered in a layer of clay from the Cretaceous-Tertiary, or K-T,
boundary in eastern Montana. (K is used as the abbreviation for
Cretaceous because C was already taken by the Carboniferous; today, the
border is formally known as the Cretaceous-Paleogene, or K-Pg,
boundary.)
The next clue showed up in south Texas, in a curious layer of end-
Cretaceous sandstone that seemed to have been produced by an
enormous tsunami. It occurred to Walter Alvarez that if there had been a
giant, impact-induced tsunami, it would have scoured away shorelines,