Catastrophic asteroid impacts are gaining a credible edge over violent volcanic eruptions as the greatest killers Earth has ever seen, according to two pieces of scientific detective work reported in tomorrow’s issue of the journal Science.

The first cataclysm in question occurred about 250 million years ago, when according to the fossil record more than 90 percent of Earth’s marine species and 70 percent of life on land perished. The event is known as the Permian-Triassic (P-T for short) mass extinction, named because it falls on the boundary between the two geological eras.