There have been five big mass extinctions in the history of the Earth. One 65 million years ago wiped out the dinosaurs, but the greatest of all happened around 251 million years ago, at the end of the Permian period. In this cataclysm at least 90 per cent 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 the impact of a huge meteorite, or prolonged volcanic eruption in Siberia? The evidence is assembled and Michael Benton gives his verdict. "When Life Nearly Died" does more than document this catastrophic event - it is also a history of developing ideas, explaining how we know what we know about geology and palaeontology, and laying bare the arguments and egos of scientists. Benton shows that this is not an arcane story of interest only to the scientific community - the implications of this mass extinction millions of years ago for the present-day biodiversity crisis are very relevant, so that the past can truly be a guide to the present and future life on Earth.