Geologists may be closer to discovering the precise date and cause of the largest and most mysterious extinction event in Earth's history, thanks to volcanic rocks in China. The Permian mass extinction is marked by the loss of 90 percent of all species a quarter-billion years ago, but scientists are split about what happened. "In order to make assumptions about any causes, you have to know when it happened and how fast it happened," said Roland Mundil of the Berkeley Geochronology Center in California. Mundil and his colleagues' work appears in a paper in the Sept. 17 edition of Science. To get a better idea of the when, Mundil's team employed a new method for measuring uranium, which predictably decays into lead over millions of years, inside zircon crystals from volcanic ash layers in rocks from Shangsi and Meishan, China.

The ash layers are from explosive volcanic eruptions and now serve as atomic clocks within layers of fossil-bearing rocks that recorded the sudden demise of most life at the end of the Permian period. But because the zircon "clocks" can leak lead, giving a false younger date, or actually be zircons mixed into the ash from older rocks, it's been difficult to extract exact dates, Mundil said.

View: Full Article | Source: Discovery Channel

Cool, so thats where they died.

Its sad but all those species had to die to mammals could inherit the Earth