Lava Dates Link Extinctions to Huge Siberian Eruption

A lava eruption over more than 100,000 square miles of Siberia could have caused climate changes that contributed to the nearly total extinction of animal life about 250 million years ago, a California researcher and others say in a study to be published today in the journal Science.

Paul R. Renne of the Institute of Human Origins in Berkeley and Asish R. Basu of the University of Rochester said laboratory dating of rock samples from the Siberian lava flow show the eruption was about the same time that fossil deposits record the extinction of up to 95% of all animal species.

“We proved that the timing of the eruption was coincident with the extinction,” Basu said in an interview. “Our work suggests a strong link between the two, but we can’t step out and say the eruption caused the extinction.”

Steven Stanley, a paleobiologist at Johns Hopkins University in Baltimore, said the study adds strength to the idea that a volcanic eruption could have caused or contributed to the early extinction, but the exact mechanism of death for millions of animals over thousands of years is still unclear.

Experts, such as Stanley, have shown that there have been a long series of major and minor extinctions in the Earth’s history. The most famous is the event 65 million years ago that killed off the dinosaurs, but the extinction 250 million years ago was even more widespread.

“It probably was the most severe global extinction on record of the past 600 million years,” said Stanley. Marine animals were the most severely affected, but the event also killed off most of the mammal-like reptile species that then walked the Earth, he said.

Basu and Renne determined when the Siberian eruption occurred by age-dating a number of rock samples taken from the site by Soviet scientists. The rocks all came from a major formation called the Siberian Lava Traps.

The specimens, Basu said, were in pristine condition with almost no weathering since they were laid down as molten lava.

To date the rocks, Basu and Renne used a technique called argon-argon aging. The technique is based on the fact that potassium decays at a known rate into argon. By measuring the ratio, the age of the rocks can be established.

Basu said the rocks consistently measured at ages of between 248.3 and 247.5 million years old, which is within the margin of error for the estimated time of the major extinction.

Lava from the massive flow covered about 130,000 square miles in successive waves that were up to a half mile thick, Basu said. The eruption continued in spurts over a period of perhaps 200,000 years and produced about 1.5 million cubic kilometers of lava rock.

Eruptions of this size would have sent millions of tons of ash, dust and gas into the atmosphere, almost certainly affecting the weather, Basu said.