Volcanic 'flood' linked to extinction

From waterfall to skyline: The rock you see is what is left of the flood

A huge outpouring of molten rock 250 million years ago may have been the decisive factor in the deaths of nearly all lifeforms on the Earth at that time.

The lava that gushed out of the ground was at least twice as extensive as previously thought, a team of international researchers now reports.

Its work suggests the "volcanic flood" was a kilometre and a half deep and covered an area half the size of Australia.

Its timing coincides with the disappearance from the fossil record of up to 90% of all marine species and 70% of land vertebrates.

Researchers suspect the upwelling released vast quantities of gas into the atmosphere, rapidly changing environmental conditions and making it impossible for most lifeforms to continue.

Wider area

Marc Reichow, from the University of Leicester, UK, and colleagues report their findings in the journal Science.

The flood basalts they studied produced the Siberian Traps, volcanic rocks found across a region of Russia called the Siberian Platform.

The Anglo-Russian research team examined rocks taken from deep boreholes in the Western Siberian Basin, nearly 1,000 kilometres west of the Siberian Platform.

From the age and chemistry of the rocks, the researchers determined that they are also part of the Siberian Traps.

The new results suggest that the total extent of the Traps covered around 3.9 million square kilometres. This is equivalent to an area just over half the size of Australia.

Later flood

The Permian-Triassic extinction is the largest, sudden disappearance of life recognised in the fossil record.

Some scientists strongly suspect the impact of an asteroid or comet may also have played a significant role.

American researchers have found chemical traces in rocks from the time which they believe point to an extraterrestrial collision.

Whatever the causes, the mass extinction is believed to have opened the way for the dinosaurs to take charge of the planet.

Their disappearance 65 million years ago has also been linked to a space impactor and another flood basalt event centred on what is now India and Pakistan.