Greenhouse Gas Eruptions Preceded Great Extinctions
By Richard A. Kerr, ScienceNOW
The biggest volcanic eruptions of the past half eon had seemed a likely culprit in the greatest mass extinction Earth has seen. Now the closest look yet at events 252 million years ago is linking those eruptions even more closely not only to the biotic cataclysm in the sea but also to the mass extinction on land.
An international group of scientists led by paleontologist Shu-zhong Shen of Nanjing Institute of Geology and Palaeontology in China intensively sampled the fossil record, they report today in Science. They examined nine rock outcrops across South China, not just the couple of sites most closely sampled in the past. Each sampling site spanned the mass extinction 252 million years ago at the end of the Permian period. The sites included records from the sea, where fully 90% of species disappeared, as well as from the land.
Shen and his colleagues also used volcanic minerals to gauge when and how fast things happened at each site. Occasional volcanic eruptions had layered minerals throughout the outcrops. In order to date these minerals, the group used the steady decay of radioactive uranium to lead. Even though the eruptions happened a quarter-billion years ago, the method gave them an error of only about 100,000 years. Improvements to the mass spectrometer that counted uranium and lead atoms and to the sample preparation procedure had reduced the dating error by a factor of four.