One of the Earth's largest extinctions was likely caused by a massive volcanic eruption that occurred in what is now southwest China more than 260 million years ago, according to a study.

The eruptions, which spewed about 500,000 cubic kilometers (120,000 cubic miles) of lava over half a million years, killed more than half of the life on the planet in the Middle Permian period, said Paul Wignal, lead author of the study in tomorrow's edition of the journal Science. That loss of life is called the Guadalupian mass extinction.

The eruptions in southwest China's Emeishan province, which left deposits of lava 200 meters (656 feet) deep in some spots, were discovered about a decade ago and Wignal and colleagues were the first to study them, he said. What they found proved to be a rarity -- direct evidence of volcanism and a massive die- off of marine life. "This link between the extinction and the volcanoes are perfect," said Wignal, 45, who teaches at the University of Leeds in Leeds, U.K., in a telephone interview yesterday.

Between the layers of igneous rock are limestone deposits holding fossilized evidence of widespread extinction, he said.

The eruption's lava flows occurred near shallow seas. The volcanic emission reacted violently as it contacted the sea water, throwing huge amounts of sulfur dioxide in the atmosphere, which led to acid rain and poor conditions for life on earth, Wignal said.

Cold and Dark

"It would have been severe cold and darkness. There'd be a lot of plant life that would be struggling," he said. While the Guadalupian extinction is dwarfed by the Permian- Triassic mass extinction, which wiped out 90 percent of marine and 70 percent of land species about 250 million years ago, the former is likely the second-largest event in the world's history, said Paul Renne, a geology professor at the University of California, Berkeley. "It's not the poster child of mass extinctions, compared with late Permian," Renne said in a telephone interview. "But it turns out to be the second-most massive extinction we know about in the geological record."

After the eruptions, it took another 500,000 years for life to return to the same level as before, Wignal said.