PALEONTOLOGY: Biggest Extinction Hit Land and Sea

Two hundred and fifty million years ago, at the end of the Permian period and the opening of the Triassic, 85% of the species in the sea vanished in a geologic moment of less than half a million years. Now from South Africa comes evidence that the Permian-Triassic extinction of land plants was equally brutal and swift. In a paper on page 1740 of this issue of Science, researchers report that rocks that started as sediments laid down in South Africa's Karoo Basin 250 million years ago tell of an abrupt switch in style of sedimentation, as if the land had been permanently stripped of the rooted plants that held it in place. But in the absence of any trace of an impact, researchers are groping for an equally far-reaching explanation.