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.
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