The Permian extinction was the biggest mass extinction event in the history of life. It has been known since the work of geologist John Phillips in the 1840s that the end of the Permian period was marked by a major turnover in marine animal species; only recently, however, have the magnitude, and the causes, of this turnover become apparent.

According to dates published in 2004, the Permian extinction occurred 252.6 million years ago and marked the end of the Permian period and the Paleozoic era. Paleontologist Douglas Erwin called it the "mother of all extinctions." Approximately 90 percent of species died during and immediately after this event (in the early Triassic period). In contrast, the extinction event that occurred at the end of the Cretaceous, and which exterminated the dinosaurs and many other species (Cretaceous extinction) killed only about 50 percent of the species on Earth. Life on Earth recovered from the Permian extinction event, but it took nearly 100 million years to regain its former diversity. Though the major groups of organisms that had dominated the Earth during the Permian (such as seed plants, mollusks, fishes, amphibians, and reptiles) survived, most of the species did not; the Triassic period began with a vastly impoverished set of species, and the later Triassic had an almost entirely new set of species within these groups.

Geological deposits that span the boundary between the Permian and Triassic periods are found in China, the Karoo Basin of South Africa, and in Russia. The interpretation of the information from these deposits needed to await the refinement of radiometric dating methods. There was worldwide evidence of a massive turnover in species makeup, but only by precise radiometric dating could scientists be sure that this turnover had happened at the same time all over the world, at or immediately after the Permo-Triassic boundary. It also awaited geopolitical developments that allowed scientific teams from Russia and America, and China and America, to work together on detailed studies. . .

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