The most intriguing new evidence about the end-Permian mass extinction comes from the field of geochemistry. Perhaps the most relevant geochemical changes are the shifts in carbon isotopes found in rocks (specifically, the ratio of carbon 12 to carbon 13). This fact indicates that, apparently, more organic matter was being buried during the late Permian than in previous times.

Although this burial of carbon is telling us something about geochemical changes during the end-Permian extinction, it is not entirely clear what. It may have to do with the sudden, deadly drop in sea level. During the early Permian, the continents merged to form the single supercontinent Pangaea. Around the continental shelves, reefs and other shallow-water communities thrived. Then, near the end of the Permian, the sea level fell. (No one knows exactly why, but it may have been caused by changes in the earth's mantle that enlarged the ocean basins.) The drop disrupted the habitats along the shore. With more of Pangaea's continental shelf exposed, greater erosion and oxidation of organic matter probably occurred. This oxidation reduced the oxygen and increased the carbon dioxide in the atmosphere, which may have humidified the planet and warmed it by as much as two degrees Celsius." [See chart ]

Scientific American, 7/96, p 76.

The Mother of Mass Extinctions, Douglas E. Erwin