The Great Dying: first it warmed, then it burned

[DainBramaged]

Recently, we discussed evidence that the Earth's biggest mass extinction, the End Permian (often called the Great Dying), was triggered by a physiological crisis: high levels of atmospheric carbon dioxide lowered the ocean's pH and created problems with anoxia. That doesn't, however, tell us much about what happened on land or about how quickly events transpired. Now, researchers have provided the most precise dates yet on the Great Dying and found that it took place over less than 200,000 years and was accompanied by very rapid changes in the atmospheric carbon dioxide.

The published dates for the End Permian roughly agree—it happened about 250 million years ago—but they use different methods and sites to arrive at those dates. The different sites shouldn't affect the dating, but they could include different ecosystems. If the timing of the mass extinction isn't uniform across these sites, it's easy to see how they could produce different dates.

The new study attempts to cut down on the uncertainty through volume: 300 samples were dated from 29 different volcanic ash beds in South China. Combined, these sites cover ocean, transitional, and terrestrial environments.

The uranium-lead dating used in these studies has a standard error of between 60-120 Kyrs (Kilo-years). However, with so many different samples, the authors were able to narrow the range of the extinction down to about 200,000 years, not much more than the error in the technique. In the end, they place the extinction at just over 252 million years ago.

http://arstechnica.com/science/news/2011/11/the-great-dying-first-it-warmed-then-it-burned.ars