Washington, DC – Volcanic eruptions in Siberia 251 million years ago may have triggered high levels of hydrogen sulfide in the oceans and atmosphere and the largest mass extinction event in Earth’s history, according to a Penn State geoscientist.
Geology professor Lee R. “Recent dating of Siberian trap volcanoes contemporary with the Permian extinction suggests that they were the trigger for the environmental events that caused the extinction,” says Kump. “But the warming caused by carbon dioxide emissions from these volcanoes would not be large enough to cause mass extinction on its own.”
However, that warming could trigger a chain of events that would lead to mass extinction. 95 percent of all species on Earth went extinct during the end-Permian extinction, while only 75 percent became extinct during the KT when dinosaurs disappeared, apparently due to a large asteroid.
Volcanic carbon dioxide will cause atmospheric warming which will, in turn, warm surface ocean waters. Normally, the deep ocean gets oxygen from the atmosphere at the poles. There the cold water absorbs oxygen from the air and because cold water is dense, it sinks and slowly moves toward the equator, taking the oxygen with it. The warmer the water, the less oxygen will dissolve and the slower the water will sink and move toward the equator.
“Warmer water slows down the conveyor belt and brings less oxygen to the deep oceans,” Kump says.
The constant rain of organic debris produced by marine plants and animals requires oxygen to decompose. With less oxygen, less organic matter is consumed aerobically.
“Today, there is not enough organic matter in the oceans to be anoxic,” Kump says. “But in the Permian, if volcanic carbon dioxide warming reduces marine oxygen, especially if atmospheric oxygen levels are low, the oceans will become deoxygenated.”
Once the oxygen runs out, the oceans become zones of bacteria that get their oxygen from sulfur oxide compounds. These bacteria strip oxygen from the compounds and produce hydrogen sulfide. Hydrogen sulfide kills aerobic organisms.
Humans can smell hydrogen sulfide gas in the parts per trillion range, the smell of rotten cabbage. Today in the depths of the Black Sea, hydrogen sulfide is present at about 200 parts per million. It is a toxic brew in which any aerobic, oxygen-requiring organism will die. For the Black Sea, hydrogen sulfide remains at depth because our rich oxygen atmosphere mixes with the upper layer of water and controls the diffusion of hydrogen sulfide upward.
At the end of the Permian, as atmospheric oxygen levels fell and hydrogen sulfide and carbon dioxide levels increased, the upper levels of the oceans could have been catastrophically enriched with hydrogen sulfide. This will kill most of the marine plants and animals. Hydrogen sulfide spreading into the atmosphere would destroy most terrestrial life.
“Hydrogen sulfide environments are better suited to extinction than carbon dioxide-rich environments,” says Kump. “Carbon dioxide will have a profound impact on marine life, but terrestrial plants thrive on carbon dioxide, yet they are involved in extinctions.”
Another piece of the puzzle related to this extinction is that hydrogen sulfide gas destroys the ozone layer. Recently, Dr. Henk Visscher of Utrecht University and colleagues suggested that there are fossilized spores from the late Permian that show deformities, which researchers suspect were caused by ultraviolet light.
“These distortions fit into the idea that the ozone layer was damaged, allowing more ultraviolet radiation,” Kump says.
Once this process is underway, there is little in the atmosphere to dissipate the methane produced in substantial swamps over this time period. The atmosphere becomes full of hydrogen sulphide, methane and ultraviolet radiation.
The Penn State researchers and their colleagues are looking for biomarkers, indicative of photosynthetic sulfur bacteria in deep-sea sediments, to complement such biomarkers, recently reported by Clancy Grice, Curtin University of Technology, Australia, and colleagues in shallow water sediments of this era in the February 4 issue of the journal, Science. These bacteria live in places where there is no oxygen but little sunlight. They may have been in their heyday at the end of the Permian. Finding evidence of green sulfur bacteria would provide evidence of hydrogen sulfide as the cause of the mass extinction.