The Mother of Mass Extinctions; July 1996; Scientific American Magazine; by Erwin; 7 Page(s)
The 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 extinctions" 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 primarily 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 reorganization 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 Permian and early Triassic are notoriously difficult to come by. The fossil record across the boundary is plagued by poor preservation, a lack of rock to sample and other problems, including access. An extensive drop in sea level during the late Permian limited the number of marine rocks deposited on land, and many areas where the best rocks were preserved (most notably, in southern China) have been relatively hard for some geologists to reach.