Between 1980 and the early 1990s, a succession of clues pointed toward a crater somewhere around the Gulf of Mexico. Pemex, the Mexican oil company, had already taken core samples in the northern Yucatan Peninsula while looking for oil. About half a mile down, the drill brought up a peculiar green, vitrified glass.
The material was known, but nobody had made the connection. Under that half mile of limestone was a gigantic crater, about 120 to 150 miles in diameter. And it dated precisely.