New research suggests that mass extinctions need not be sudden events. The deadliest mass extinction, which occurred about 250 million years ago and is known as the “Great Dying,” took a long time to kill 90 per cent of Earth’s marine life, and it killed in stages.
The analysis, published this month in the Geological Society of America Bulletin, provides strong evidence that Earth’s biggest mass extinction phased in over hundreds of thousands of years, not at the same time as suggested in many previous studies.
“This study demonstrates that extinctions are not necessarily synchronous everywhere,” says Charles Henderson, professor in the geoscience department and co-author of the paper.
“This is very similar to current climate model predictions that suggest the Arctic will warm more rapidly than mid-latitude areas so the first effects on life related to modern climate change may well be felt in the Arctic.”
Previous investigations have focused on deposits created by a now vanished ocean known as Tethys, a kind of precursor to the Indian Ocean. Those deposits, in South China particularly, record a sudden extinction at the end of the Permian. This study explored the geology of a Permian-Triassic extinction and boundary section in the Sverdrup Basin on Ellesmere Island in the Canadian Arctic. That location, at the end of the Permian, would have been a lot closer to the Siberian traps (massive volcanic deposits) than sites in South China.
What appears to have happened, according to the researchers led by Thomas Algeo of the University of Cincinnati, is that the effects of early Siberian volcanic activity, such as toxic gases and ash, were confined to the northern latitudes. Only after the eruptions were in full swing did the effects reach the tropical latitudes of the Tethys Ocean.
The extinction in the Sverdrup Basin, in the Arctic, occurred about 100,000 years before the extinctions in China as revealed by detailed correlation of carbon isotopic signatures and conodont biostratigraphy.
The Canadian sedimentary rock layers studied are 24 metres thick and cross the Permian-Triassic boundary, including the latest Permian mass extinction horizon. The investigators looked at how the type of rock changed from the bottom to the top of the section. They looked at the chemistry of the rocks and they looked at the fossils contained in the rocks.
February 6, 2012
By Randy Boswell, Postmedia News
News story in the Calgary Herald on the Permian-Triassic boundary! Based on a GSA Bulletin article by Charles Henderson as second author.