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,
leaving behind a distinctive fingerprint in the sedimentary record. He scanned the records of
thousands of sediment cores that had been drilled in the oceans, and found such a fingerprint
in cores from the Gulf of Mexico. Finally, a hundred-mile-wide crater was discovered or,
more accurately, rediscovered, beneath the Yucatán Peninsula. Buried under half a mile of
newer sediment, the crater had shown up in gravity surveys taken in the nineteen-fifties by
Mexico’s state-run oil company. Company geologists had interpreted it as the traces of an
underwater volcano and, since volcanoes don’t yield oil, promptly forgotten about it. When
the Alvarezes went looking for cores the company had drilled in the area, they were told that
they’d been destroyed in a fire; really, though, they had just been misplaced. The cores were
finally located in 1991 and found to contain a layer of glass—rock that had melted, then
rapidly cooled—right at the K-T boundary. To the Alvarez camp, this was the clincher, and it
was enough to move many uncommitted scientists into the pro-impact column. “Crater
supports extinction theory,” the Times announced. By this point, Luis Alvarez had died of
complications from esophageal cancer. Walter dubbed the formation the “Crater of Doom.” It
became more widely known, after the nearest town, as the Chicxulub crater.