It's well known that the dinosaurs were wiped out 66 million years ago when a meteor hit what is now southern Mexico but evidence is accumulating that the biggest extinction of all, 252.3m years ago, at the end of the Permian period, was also triggered by an impact that changed the climate. While the idea that an impact caused the Permian extinction has been around for a while, what's been missing is a suitable crater to confirm it. Associate Professor Eric Tohver of the University of Western Australia's School of Earth and Environment believes he has found the impact crater...