Sixty-six million years ago, a massive asteroid crashed into a shallow sea near Mexico. The impact carved out a 90-mile-wide crater and flung mountains of earth into space. Earthbound debris fell to the planet in droplets of molten rock and glass. Ancient fish caught glass blobs in their gills as they swam, gape-mouthed, beneath the strange rain. Large, sloshing waves threw animals onto dry land, then more waves buried them in silt. Scientists working in North Dakota recently dug up fossils of these fish: They died within the first minutes or hours after the asteroid hit, according to a paper...