The Sixth Extinction: An Unnatural History

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.