A. MEDVEDEV Russian Academy of Sciences

The cause of the largest known mass extinction event, at the end of the Permian period 250 million years ago, remains elusive. The leading candidates for the chaos that killed close to 95 percent of marine species and 70 percent of those on land include dramatic fluctuations in climate or sea level, severe volcanism or an impact with an asteroid or comet. Now findings published in the current issue of the journal Science add further fuel to the debate. Scientists have discovered that the surge of magma that occurred at the time of the Permian extinction was at least twice as extensive as previously believed.

The giant outflow of magma produced the Siberian Traps, volcanic rocks located in an area of Russia known as the Siberian platform. Marc K. Reichow of the University of Leicester in England and his colleagues investigated rocks removed from deep within a basin located nearly 1, 000 kilometers to the west of the platform (see image). After analyzing the chemical and physical structure of these samples, the team determined that the rocks came from the same source as did those in the Siberian Traps. The new findings suggest that the Siberian Traps in fact covered almost 3.9 million square kilometers, an area approximately half the size of Australia, over the course of hundreds of thousands of years. Such an increased flux of magma at the close of the Permian would have added substantially to the volume of climate-changing gases released into the atmosphere. Indeed, the team concludes that "the larger area of volcanism strengthens the link between the volcanism and the end-Permian mass extinction."