251 million years ago, at the end of the Permian period, life on Earth was almost completely wiped out by an environmental catastrophe of a magnitude never seen before or since. All over the world complex ecosystems were destroyed. In the sea, coral reefs, fishes, shellfish, trilobites, plankton, and many other groups disappeared. On land, the sabre-toothed gorgonopsian reptiles and their rhinoceros-sized prey, the dinocephalians and pareiasaurs, were wiped out forever. Only 5 per cent of species survived the catastrophe, and for the next 500,000 years life itself teetered on the brink of oblivion. What terrible event could have wrought such havoc? Two theories have been proposed - the impact of a huge meteorite or comet over 10 kilometres in diameter, or a massive and prolonged volcanic eruption. Up to now the evidence has been equivocal. But the data has been accumulating over the past 10 years, and the picture is now clear enough to say with some certainty what happened.
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