Extraterrestrial impacts: The big splash

Seventy per cent of the Earth is covered with sea water, and most of that is ocean, so most of the large asteroids and comets striking the planet should hit deep water. But very little remains of these impacts — virtually all evidence of large impacts, in the form of craters and associated debris, is found on land. On page 357 of this issue, Gersonde et al. describe the evidence for and consequences of the impact of an asteroid, 1-4 km in diameter, in a 5,000-m-deep ocean basin, 1,500 km southwest of Chile. The asteroid hit the Earth in the late Pliocene, some 2.15 million years ago.