In a massive extinction about 250 million years ago, 90 percent of Earth’s sea creatures and up to 80 percent of its terrestrial species vanished. Some scientists attribute the Great Dying to a gigantic asteroid or comet impact, similar to one in Mexico that obliterated the dinosaurs 185 million years later. In May researchers reported they located what may be the telltale scar in a large underwater dome off Australia’s northwestern coast.
Other investigators had previously suspected something extraterrestrial about the dome, Bedout (pronounced “be-doo”) High, because its uplifted area is a common feature of impact craters. And tentative dating pegged Bedout at 250 million years old, within the ballpark of the extinction. Intrigued, geochemist Luann Becker of the University of California at Santa Barbara and her colleagues examined cores extracted from deep within the dome. They found glassy minerals with a disorganized crystalline structure characteristic of violently smashed and ...
