Some years ago, a National Enquirer headline announced that Martians had killed off the dinosaurs while visiting Earth to do some big-game hunting. It is hard to imagine such an explanation for the extinction of the trilobites - hard-shelled creatures that looked like giant woodlice. Compared with T. rex and triceratops, they lack the trophy quality. But the episode that led to the trilobites' demise was actually the greatest threat there has ever been to life on Earth. It occurred at the end of the Permian period, 251 million years ago. Over a very short time, a huge number of hitherto dominant forms of life disappeared: not only trilobites, which were already on the way out, but most classes of organism on both land and sea; all were gone for ever.

LRB 1 April 2004 | PDF Download