Washington, July 17 : A new study has found out that a surge of undersea volcanic activity about 93 million years ago sapped the oceans of oxygen, triggering a mass extinction of marine life.
According to a report in National Geographic News, the catastrophic event buried a thick mat of organic matter-from large clams to single-celled algae-on the seafloor, which today is a major source of oil.
At the time of the mass die-off, Earth's climate was warm and muggy, and ocean circulation was sluggish, according to study co-author Steven Turgeon, an earth scientist at the University of Alberta in Edmonton, Canada.
Palm trees grew on the North Slope of Alaska and carbon dioxide levels were 3 to 12 times higher than today's concentrations.
The carbon dioxide spike was mostly a result of increased volcanic activity linked to Earth's rapidly shifting tectonic plates, according to Turgeon.
"And now we have this magmatic pulse that happened at that time-a huge one by what we can tell-and that's what caused this chain reaction to drive the oxygen from the ocean and cause this mass extinction," he said.
Scientists have long suspected that undersea volcanism could be responsible for the marine mass extinction, an anoxic, or oxygen-depleting, event known as the OAE2. ut until now the evidence was "sketchy". Oceanic anoxic events starve some species of marine life of oxygen, an essential gas.
The geologic record suggests that the events occur when carbon dioxide levels are several times higher than current concentrations.
Turgeon and colleague Robert Creaser analyzed rocks in northeastern South America and central Italy that were undersea in the middle of the Cretaceous, which lasted from 145 million to 65 million years ago.
The researchers looked for evidence of the metallic element osmium, hoping that it would yield insight to the trigger of the OAE2.
One type of osmium "signature" is primarily derived from river debris that drains into the oceans. Another type comes from magmatism and extraterrestrial sources, such as meteorites and space dust, Turgeon explained.
Since there is no evidence of a meteor or comet impact 93 million years ago, a 30- to 50-fold increase in magmatism was implicated as the instigator of the mass extinction.
The surge in undersea volcanism put massive amounts of metals in the ocean. This encouraged the growth of microscopic marine plants called phytoplankton, which produced excessive organic matter.
"When the plants died, this rain of organic matter fell through the marine water column and stripped it of oxygen," said Timothy Bralower, a geoscientist at Pennsylvania State University. "And this anoxic event in the deep waters led to the extinction of the (flora and fauna) that lived on the seafloor," he added.