Extinction 250 mya Linked to Volcanic Flood

[Richard W Travsky <rtravsky@uwyo.edu>]

http://news.bbc.co.uk/hi/english/sci/tech/newsid_2030000/2030075.stm

A huge outpouring of molten rock 250 million years ago may have been the
decisive factor in the deaths of nearly all life forms 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 report.

Their 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 life forms to continue. 
...
 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.