The lavas of East Greenland form a layered sequence up to seven kilometers thick. They are the relics of massive volcanic activity that accompanied the birth of the northeast Atlantic approximately 55 million years ago.
Credit: M. Storey, Roskilde University
CANBERRA: Ancient Earth underwent intense global warming when cataclysmic volcanic eruptions pushed Greenland from northwest Europe.
The prehistoric catastrophe may help put current global warming in perspective, geologists say.
About 55 million years ago Earth underwent a period of intense warming, called the Paleocene-Eocene thermal maximum (PETM), lasting up to 220,000 years. During this time, sea surface temperature rose by 5°C in the tropics and 6°C in the Arctic - and ocean acidity increased.
Deep-water ocean life was snuffed out by large amounts of plankton near the surface blocking light and oxygen filtering down to the level of fish, which became extinct. However, until now scientists did not know the cause of the warming.
A study published today in the U.S. journal Science adds evidence that this temperature rise occurred due to greenhouse gases released during intense volcanic activity. This activity was so great it separated Greenland from Europe, covered the ocean floor with huge amounts of lava, and effectively formed the North Atlantic Ocean in the process.
The eruptions were an example of a 'flood basalt eruption' – a kind of volcanic activity that can spew out 100 times as much lava as any eruption in recorded history. The thousands of eruptions that follow can create lava deposits millions of cubic kilometres in size.
Along with this monumental outpouring of lava, more than 1,500 gigatonnes of greenhouse gases methane and carbon dioxide were released into the oceans and atmosphere.
"Marine records [show] a sudden release of carbon dioxide," said geologist Carl Swisher, from Rutgers in New Jersey, U.S. and study co-author. "Now, for the first time, geologists have a precise correlation to link the sudden increase in volcanic activity and spike in greenhouse gases."
"There has been evidence in the marine record of this period of global warming and evidence in the geological record of the eruptions at roughly the same time, but until now there has been no direct link between the two," added Robert Duncan, a co-author at Oregon State University in Corvallis.
The team was able to link the ancient warming to the volcanic eruptions by dating rocks. They collected volcanic ash from marine sediments southwest of the U.K., and calculated their age from the known rate of radioactive decay of potassium and argon in the material.
"I think the dating is quite good," commented Paul Renne of the Berkeley Geochronology Centre in California, in a related news article also in today's Science. It "certainly provides strong linkage between the PETM and the [volcanic activity]."
The release of greenhouse gases was probably the result of the intense volcanic activity heating old sedimentary deposits that contained large amounts of decayed organic matter, said the authors. Heating these carbon-rich sediments would have driven off methane and carbon dioxide into the atmosphere.
They characterize this spike in worldwide sea temperatures and acidity as an ancient "planetary emergency" - but today's situation may be much worse. During the PETM, it took 10,000 years to release that amount of carbon - and more than 100,000 years passed before carbon dioxide levels in the atmosphere returned to their previous level.
Today, emissions from fossil fuels are contributing approximately 7 gigatonnes of carbon dioxide in to the atmosphere each year - a rate that far exceeds what happened 55 million years ago.
