A massive release of greenhouse gases likely caused the world’s worst extinction, according to an international team that has been poring over the remains.

About 95 per cent of Earth’s marine life and 70 per cent of terrestrial species were wiped out as wildfires roared across the world, oceans acidified, and temperatures soared more than 250 million years ago, the scientists say.

And the evidence points to a “runaway greenhouse event,” says geoscientist Charles Henderson, of the University of Calgary.

He is the Canadian co-author of the study, to be published today in the journal Science, that gives the most detailed picture yet of how the Permian mass extinction unfolded.

Henderson says it is important to understand what happened, given the concerns that modern greenhouse gas emissions might also trigger runaway global warming.

Carbon dioxide from burning fossil fuels is the big concern today. In the Permian, the scientists say volcanoes appear to have been the culprit, releasing “massive” amounts of CO2 and methane, a potent greenhouse gas.

Henderson says red-hot lava spewed across a region the size of Western Europe at the end of the Permian, when there was just one land mass called Pangea and the continents had not yet formed.

He says the enormous lava flows would have ignited coal and other combustibles, sending carbon dioxide wafting into the atmosphere and also may have melted frozen gas hydrates and released huge stores of methane.

“It then cascades into this series of disasters that continue until most things are extinct,” says Henderson.

He says the geological and fossil record point to several possible “kill mechanisms” as the disaster unfolded, including fires, acidification, as well as loss of oxygen in the oceans, and perhaps even hypercapnia, which sees too much CO2 build up in the blood and can be lethal.

The research team, led by Shu-zhong Shen at China’s Nanjing Institute of Geology and Paleontology, has spent years combing through the evidence preserved in sedimentary rocks and volcanic ash beds at several locations in China that formed as the extinction unfolded. The scientists found the distinct signature of “widespread wildfires” and changes in the ocean chemistry that coincide with a spike in carbon 12, a form of carbon common to volcanoes and gas hydrates.

They also looked at 1,450 species, from fish to ferns, that vanished during the extinction, which peaked 252 million years ago and took close to 200,000 years to play out.

Small eel-like creatures, called conodonts, helped the researchers piece together what transpired, says Henderson, who visits China each year to collect and to study fossils of the creature’s tiny teeth.

“We can use them as time clocks,” says Henderson, who is also charting the evolution and fate of conodonts in the Arctic and in Western Canada.

He says the world’s climate at the end of the Permian changed dramatically. “It went from basically like today, where you had hot tropics and cooler polar regions, to a world in which everything was a tropics,” he says.

The Permian extinction may have been “catastrophic,” the scientists say, but it did not happen overnight.

They say it took thousands of years for the species to die out, with the bulk of the extinctions likely occurring over a 20,000-year period.

“These things take time,” says Henderson, who notes that environmental changes caused by humans’ everincreasing use of fossil fuels are also expected to occur gradually. “We don’t need to panic,” he said, “but maybe we need to be more prudent about our use of carbon-based fuels.”