The greatest mass extinction in Earth's history happened some 251 million years ago. In this cataclysm at least 90% of life was killed, both on land and in the sea, almost bringing evolution to a halt.What caused destruction on such an unimaginable scale?Was it the impact of a huge meteorite, or prolonged volcanic eruption in Siberia? In this acclaimed book, newly available in paperback, Michael Benton assembles all the evidence and gives his verdict.