Approximately 250 million years ago, vast numbers of species disappeared from Earth. This mass-extinction event may hold clues to current global carbon cycle changes, according to Jonathan Payne, assistant professor of geological and environmental sciences. Payne, a paleobiologist who joined the Stanford faculty in 2005, studies the Permian-Triassic extinction and the following 4 million years of instability in the global carbon cycle. In the July issue of the Geological Society of America Bulletin, Payne presented evidence that a massive, rapid release of carbon may have triggered this extinction.
"People point to the fossil record as a place where we can learn about how our actions today may affect the future course of evolution," Payne said. "That's certainly true: The deep geologic record provides context for modern events. We may miss very important processes or underestimate the magnitude of changes in the future by using only the past couple thousand years as a baseline."
Great Bank of Guizhou
Payne has spent the past five years unearthing the deep geologic record in south China. The kilometer-thick, limestone fossil beds at the Great Bank of Guizhou formed in shallow ocean waters during the late Permian and early Triassic periods. As the ocean floor sank, new, younger layers of limestone formed on top of deeper, older ones. Since then, plate tectonics have turned these rocks on their side. Now, Payne and his colleagues can walk back in time across the formerly horizontal layers.
Marine fossil beds such as these offer two advantages for someone studying broad patterns in the history of life, according to Payne. Because ocean waters cover large areas for long periods of time and somewhat protect the underlying rocks from erosion, marine fossil beds tend to be physically larger and cover a longer period of time with finer temporal resolution.