Global extinction was not a sudden event

About 252 mn years ago, at the end of the Permian period, Earth almost became a lifeless planet.

Washington: Most of the life forms wiped out in an event known as the Great Dying, 250 million years ago, came slowly from thousands of centuries of volcanic activity.

The deadliest mass extinction of all took a long time to kill 90 percent of Earth`s marine life, and it killed in stages, according to a detailed investigation by an University of Cincinnati team, led by professor of geology Thomas J. Algeo.

Algeo worked with 13 co-authors to produce a high-resolution look at the geology of a Permian-Triassic boundary section on Ellesmere Island in the Canadian Arctic, the journal Geological Society of America Bulletin reports.

About 252 million years ago, at the end of the Permian period, Earth almost became a lifeless planet. Around 90 percent of all living species disappeared then in what scientists have called `The Great Dying`.

Algeo and colleagues have spent much of the past decade investigating the chemical evidence buried in rocks formed during this major extinction, according to a Cincinnati statement.

The world revealed by their research is horrific and alien -- a devastated landscape, barren of vegetation and scarred by erosion from showers of acid rain, huge "dead zones" in the oceans, and runaway greenhouse warming leading to sizzling temperatures.

The evidence that Algeo and colleagues are looking at points to massive volcanism in Siberia. A large portion of western Siberia reveals volcanic deposits up to five km (three miles) thick, covering an area equivalent to the continental US. And the lava flowed where it could most endanger life, through a large coal deposit.

What appears to have happened, according to Algeo and his colleagues, is that the effects of early Siberian volcanic activity, such as toxic gases and ash, were confined to the northern latitudes. Only after the eruptions were in full swing did the effects reach the tropical latitudes of the Tethys Ocean.

"The eruption released lots of methane when it burned through the coal," Algeo said. "Methane is 30 times more effective as a greenhouse gas than carbon dioxide. We`re not sure how long the greenhouse effect lasted, but it seems to have been tens or hundreds of thousands of years."