NASA scientists have identified a 125-mile-wide crater off the coast of Australia as the likely impact site of a giant meteorite that almost wiped out life 250 million years ago.
A team of U.S. scientists said Thursday they believe the Bedout (pronounced Beh-DOO) crater is where a 6-mile-wide meteorite hit, triggering the Permian-Triassic extinction that erased about 90 percent of marine and 70 percent of land species.
Extinctions are a fact of life, erasing many species en masse at least six times over the past 550 million years, most famously in the dinosaur extinction 65 million years ago.
Scientists once attributed the earlier extinction — which took place at the boundary of the Permian and Triassic geologic periods — to a massive burst of volcanic activity or sudden climate change, but evidence of an impact-triggered catastrophe has grown.
"I think we have a convincing case" that a meteorite triggered that extinction, says geologist Luann Becker of the University of California-Santa Barbara. A report by Becker's group, due to be published in the journal Science, describes melted rock and fractured quartz deposits in core samples from Bedout that are consistent with such an impact.
Ironically, the Permian-Triassic mass extinction cleared the way for the dinosaurs that were wiped out in a later meteorite strike. NASA and the National Science Foundation, which funded the new study, are interested in how evidence of past strikes can help people prepare for future ones.
During the Permian era, all of today's continents were joined in a supercontinent called Pangea, dominated by long-legged reptiles and surrounded by an ocean filled with shelled creatures and sea lilies. The melted rock filling the Bedout crater likely released soot and sulfur that polluted the atmosphere and the oceans, triggering catastrophic climate change, Becker's team suggests.
Bedout was first identified as a crater in 1996. Becker's team suggests the impact there may have touched off widespread volcanic eruptions in Siberia.
Becker speculates the breakup of Pangea, whose pieces drifted apart to form today's continents, may have been caused by the double whammy of asteroid impact and volcanoes.