Some 250 million years ago, 90% of life on earth was wiped out. It was the greatest mass extinction ever. What caused this catastrophe? In this revised and expanded edition of a classic account, Michael J. Benton assesses the competing claims for a meteorite impact or a volcanic eruption in Siberia and brings the story thoroughly up to date. Hundreds of geologists and palaeontologists have been investigating all aspects of this astonishing event, conducting fieldwork around the world, especially in South China and Russia. New details allow us to demonstrate the close tie between the acid rain crisis on land and the anoxia in the oceans. Importantly, our view of the timing of the crisis has advanced enormously, with not only far greater precision in dating, but also the demonstration that there were two peaks of extinction, and then repeated crises for 5 million years afterwards. A great deal of new research has focused also on the slow recovery of life to a more normal state. New sections explore how the great Mesozoic sea dragons became established at the tops of the marine food pyramids, and how, unexpectedly, the crisis set in motion one of the greatest events in palaeontological history: the origin of the dinosaurs.