Roughly 252 million years ago, life on the earth nearly ceased to exist--as much as 90 percent of marine life and 70 percent of terrestrial life died out. At around the same time, a vast up swelling of magma covered between one million and four million cubic kilometers of what is now Siberia. The eruption continued off and on for about a million years, with basalt lava and poisonous gases seeping up through cracks in Siberia's mantle. Now rocks from Italy may have linked the two events.
In a paper in the current issue of Geology, Mark Sephton of Imperial College London and his colleagues reveal that sedimentary rocks from that period--when they were on the bottom of a shallow sea--contain a pulse, or unusually elevated levels of organic material from soil and plants. Typically microbes break down this material immediately. These rocks suggest, however, that a great flood of such terrestrial organic matter reached the sea and essentially swamped it, suffocating marine life. "Similar to the 'dead zone' nowadays spreading in the Gulf of Mexico, the soil crisis could have caused a worldwide expanse of uninhabitable low-oxygen conditions in shallow waters," explains team member Henk Visscher of Utrecht University in the Netherlands.
How did all of this soil make it into the sea? The researchers argue that the deadly gases of the Siberian eruption killed vegetation across the globe, just as much smaller modern eruptions have produced acid rain and other plant-killing phenomena. Without roots to hold the soil in place, rivers and streams washed most of the dead vegetation to the sea where it then blocked the sun's light and sucked up all the oxygen. "What began on land ended in the sea," Visscher says. "It seems there was no place to hide at this time of great dying."
Although this linkage may not end the debate over what caused the earth's greatest mass extinction, it stands to shed light on the loss of life the planet is currently experiencing. "Land degradation is a worsening global problem thanks to human activity and soil erosion [that] has caused the loss of a third of arable land over the last 40 years," Sephton notes. "Identifying the nature of the end of Permian soil crisis may help us understand what is in store for us in the years ahead."