The greatest mass extinction in Earths history happened some 251 million years ago. In this cataclysm at least 90 percent of life was killed both on land & 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 & gives his verdict.