Geologists Link the "Great Dying" to Volcanism

Science & Technology at Scientific American.com: Geologists Link the "Great Dying" to Volcanism: Modified:
"Life on Earth almost died out about 252 million years ago. Roughly 90% of marine life and 70% of terrestrial life died out. At roughly the same time, a vast up swelling of magma on land that became Siberia covered between one million and four million cubic kilometers. Eruption continued for about a million years, with basaltic lava and poisonous gases emerging through cracks in Siberia's mantle. Rocks from Italy may have linked the extinctions with the massive upwellings of magma.

In a paper in the Dec '05 issue of Geology, Mark Sephton of Imperial College London and his colleagues reveal that sedimentary rocks from that period, formed on the bottom of a shallow sea, contain unusually elevated levels of organic material from soil and plants. Typically microbes break down suchmaterial immediately. However, these rocks suggest, that a great flood of such terrestrial organic matter reached the sea, swamping it and 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.

The researchers argue that deadly gases emitted during the Siberian eruption killed vegetation across the globe. Without roots to hold the soil in place, rivers and streams would have carried most of the dead vegetation to the sea where it then blocked the sun's light and consumed 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 postulated 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.""

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