University of Alberta: Volcanic eruptions wiped out marine life 93 million years ago

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Scientists previously reported that mass extinctions occurred in the past mainly due to asteroids hitting the earth, wiping out plants and animals. However, it was never attributed to forces within the earth until now.

Steven Turgeon, a researcher from the University of Alberta Earth and Atmospheric Science Department, claims mass extinction occurred 93 million years ago and it was primarily due to high volcanic activities in the depths of the ocean.

Turgeon and fellow researcher Robert Creaser said massive lava eruptions altered the chemistry of the sea and blanketed the sea floor with thick layers of organic matter, which later became a major source of oil. The eruptions may have also caused disturbances in the atmosphere.

Turgeon told Physorg:

"It certainly caused an extinction of several species in the marine environment...It wasn't as big as what killed off the dinosaurs, but it was what we call an extreme event in the Earth's history, something that doesn't happen very often."

Turgeon and Creaser found evidence of high levels of the element osmium, which is an indicator of volcanism in seawater. They found it in black shale-rocks drilled off the coast of South America and in the mountains of central Italy.

Turgeon added:

"Because the climate was so warm back than, the oceanic current was very sluggish and it initially buffered this magmatic pulse, but eventually it all went haywire...The oxygen was driven from the ocean and all the organic matter accumulated on the bottom of the sea bed, and now we have these nice, big, black shale deposits worldwide, source rocks for the petroleum we have today."

Researchers said the eruptions occurred within 23,000 years of mass extinction at that time. Initially, because of the eruptions, nutrients were released which helped plants and animals immensely. But once the organisms died, they blanketed the sea, depleting its oxygen levels. This caused the release of carbon dioxide into the oceans and atmosphere, and as a result, oxygen levels on Earth were depleted, causing mass extinction.

Scientists call them "anoxic events," where oxygen is deprived. But luckily, these anoxic events are very rare in nature. They occur only when there are elevated levels of carbon dioxide and a very warm climate over extended periods.

The anoxic event, however, had an odd-side effect; it helped the climate cool down and it actually dropped carbon dioxide levels.

"Organic matter that's decaying returns components like carbon and CO2 to the atmosphere...But this event locked them up at the bottom of the ocean, turning them into oil, drawing down the CO2 levels of the ocean and the atmosphere."

About 10,000-50,000 years later, carbon dioxide levels rose again, leading to further global warming and extinction.

Turgeon and Creaser hope their study will help us better understand global warming theories. Their research paper will appear this Thursday in the weekly science journal Nature.