From “Date and Rate of Earth’s Most Extreme Extinction Pinpointed: Results Stem from Largest Ever Examination of Fossil Marine Species” (ScienceDaily, Nov. 17, 2011), we learn:
It’s well known that Earth’s most severe mass extinction occurred about 250 million years ago. What’s not well known is the specific time when the extinctions occurred. A team of researchers from North America and China have published a paper in Science which explicitly provides the date and rate of extinction.
At that time 95% of marine life and 70 percent of land life went extinct.
Through the analysis of various types of dating techniques on well-preserved sedimentary sections from South China to Tibet, researchers determined that the mass extinction peaked about 252.28 million years ago and lasted less than 200,000 years, with most of the extinction lasting about 20,000 years.
The researchers think that some sort of global warming may have triggered the biomass collapse, especially
… the trigger, as suggested by these researchers and others, was the massive release of CO2 from volcanic flows known as the Siberian traps, now found in northern Russia.
It will be interesting to see whether further evidence supports such a precise dating.