Scientists at the University of Calgary say the discovery supports the theory that massive volcanic eruptions burned significant volumes of coal, producing ash clouds that could have triggered runaway global warming 250 million years ago, wiping out 95 percent of life in the seas and 70 percent of land creatures, a university release said Monday.
Unlike the extinction of the dinosaurs 65 million years ago, generally believed to have been caused by the impact of a meteorite, it is unclear what caused the so-called late Permian extinction.
Some scientists have suggested massive volcanic eruptions bursting through coal beds in Siberia would generate significant greenhouse gases.
"Our research is the first to show direct evidence that massive volcanic eruptions -- the largest the world has ever witnessed -- caused massive coal combustion, thus supporting models for significant generation of greenhouse gases at this time," Steve Grasby of the university's Department of Geoscience said.
The volcanoes, known as the Siberian Traps, are located in northern Russia in a region covering about 750,000 square miles, an area greater than that of Europe.
The ash plumes would have covered much of the world, including regions in Canada's arctic where coal-ash layers were found.
"It was a really bad time on Earth," Grasby said. "In addition to these volcanoes causing fires through coal, the ash it spewed was highly toxic and was released in the land and water, potentially contributing to the worst extinction event in earth history."