Global warming - 55m years ago
Updated on 29 April 2007
A period of intense global warming 55 million years ago was caused by massive volcanic eruptions that split apart Greenland and north-west Europe, scientists believe.
New research shows how the volcanic activity boosted ocean temperatures by up to 6C and led to a rise in sea levels.
The findings will help scientists better understand the Earth's response to the release of man-made greenhouse gases today.
Experts already knew about the prehistoric heatwave, which lasted about 220,000 years and is called the Palaeocene-Eocene Thermal Maximum (PETM). But until now the phenomenon has not been firmly linked to the outpouring of greenhouse gases by volcanic fissures.
"That prehistoric volcanic activity released more than 2,000 gigatonnes (billion metric tons) of carbon into the oceans and atmosphere in the form of methane and carbon dioxide - two potent greenhouse gases," said Dr Michael Storey, from Roskilde University in Denmark, one of the geologists whose research has been reported in the journal Science.
Precise dating techniques matched a layer of volcanic ash covering ocean floor sediments from the PETM era with a layer in East Greenland and the Faroe Islands, north of Scotland.
Here, the ash overlies layers of basaltic lava up to seven kilometres thick left over from the eruptions.
The lava flowed in huge quantities from cracks in the Earth's crust that split a whole continent in two. Some 10 million cubic kilometres of magma were brought up from below the Earth's surface.
During the PETM ocean acidity increased and large numbers of deep sea creatures became extinct.
Co-author Professor Robert Duncan, from Oregon State University in the US, said: "We think the first volcanic eruptions began about 61 million years ago and then it took another five million years for the mantle to weaken, the continent to thin and the molten material to rise to the surface. It was like lifting a lid. The plate came apart and gave birth to the North Atlantic Ocean."
http://www.sciencemag.org(Science)
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