Erwin - 72 S cientific A merican July 1996 The Mother of...

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Unformatted text preview: 72 S cientific A merican July 1996 The Mother of Mass Extinctions Disaster struck 250 million years ago, when the worst decimation in the earth’s history occurred. Called the end-Permian mass extinction, it marks a fundamental change in the development of life by Douglas H. Erwin PATRICIA J. WYNNE 1 DROP IN SEA LEVEL, which had begun gradually about 260 million years ago, be- came quite sudden at the very end of the Permian, destroying near-shore habitats and destabilizing the climate. 2 INCREASED OXIDATION of organic matter raised levels of carbon dioxide in the atmo- sphere, contributing to global warming and depleting the amount of oxygen that could dissolve in water. FORAMINIFERA RUGOSE CORALS Copyright 1996 Scientific American, Inc. T he history of life on the earth is replete with catastrophes of varying magnitudes. The one that has captured the most attention is the extinction of the dinosaurs and other organisms 65 million years ago—between the Cretaceous and Tertiary periods—which claimed up to half of all species. As severe as that devastation was, it pales in comparison to the greatest disaster of them all: the mass extinction, some 250 million years ago, at the end of the Permian period. Affectionately called “the mother of mass ex- tinctions” among paleontologists (with apologies to Saddam Hussein), it yielded a death toll that is truly staggering. About 90 percent of all species in the oceans disappeared during the last several million years of the Permian. On land, more than two thirds of reptile and amphibian families vanished. Insects, too, did not escape the carnage: 30 percent of insect orders ceased to exist, marking the only mass extinction insects have ever undergone. But from catastrophes, opportunities arise. For several hundred million years before the end-Permian event, the shallow seas had been dominated by life-forms that were primar- ily immobile. Most marine animals lay on the seafloor or were attached to it by stalks, filtering the water for food or waiting for prey. In the aftermath of the extinction, many once minor groups—active, predatory relatives of modern-day fish, squids, snails and crabs—were able to expand. Some completely new lineages appeared. This ecological re- organization was so dramatic that it forms a fundamental boundary in the history of life. Not only does it demarcate the Permian and Triassic periods, it also establishes the close of the Paleozoic era and the start of the Mesozoic era. The modern tidal pool reflects S cientific A merican July 1996 73 DEADLY CATASTROPHES combined to wipe out most of life on the earth at the end of the Permian period, about 250 million years ago. Reef and shallow-water communities, consist- ing of corals, sea lilies, foraminifera and other organisms, were especially hard hit. On land, more than two thirds of reptiles and amphibians and nearly one third of insects disappeared....
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This note was uploaded on 02/08/2011 for the course EAS 1601 taught by Professor Lynch during the Spring '08 term at Georgia Tech.

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Erwin - 72 S cientific A merican July 1996 The Mother of...

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