THE discovery of an ancient crater off the north-west coast of Australia may explain the largest mass extinction of species the Earth has ever seen. It also raises intriguing questions about how catastrophic events combine to wipe out huge numbers of species.

At the end of the Permian period, around 251 million years ago, over 90 per cent of marine species died away as well as 50 to 70 per cent of land species.

Now researchers studying an undersea mound called the Bedout High have found what they think is evidence of a meteorite impact that dates to the end of the Permian (Science, DOI: 10.1126/science.1093925). The structure shares some features with the Chicxulub crater off the coast of Mexico, which many believe is the site of a meteorite impact that wiped out the dinosaurs 65 million years ago.

Intriguingly, the timing of the impacts at both these sites coincides with huge volcanic activity elsewhere on the globe. "This is begging for an explanation, and to date no one has found one," says Andy Saunders, a geologist at the University of Leicester in the UK.

Luann Becker at the University of California, Santa Barbara, and her colleagues who investigated Bedout High suggest that ripples in the Earth's crust caused by the impact might have triggered eruptions in a region predisposed to volcanoes. But Saunders says that there needn't be any link. Perhaps mass extinctions only occur when large impacts happen to coincide with extreme volcanic activity, he says.

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