5 million-year hangover
Scientists say climate change slowed recovery after the world’s greatest extinction event 250 million years ago
By Spencer Hunt | THE COLUMBUS DISPATCH
Imagine an overheated Earth where the oceans have become steaming pools of acid and most plants and animals are extinct. • This is no doomsday vision of the future. Our planet went through this exact scenario 250 million years ago during a time that scientists call the Great Dying. • The world’s greatest extinction event wiped out 90 percent of life in the oceans and about 70 percent on land. • Earth did recover, but it took about 5 million years, according to a team of earth scientists, including Ohio State University geologist Matthew Saltzman. • “That’s a relatively long amount of time,” he said. “We see mass extinctions throughout Earth’s history and, in most cases, the recovery took place in about 1 million years or so.” • The researchers say they have unraveled the mystery of this 5-million-year hangover. The answer, they say, is climate change.
This fossil of a Crinoid, a starfish relative that lived at the time of the great Permian extinction, is in Ohio State’s Orton Geological Museum.
The same phenomenon that climatologists today link to the burning of fossil fuels played an integral role in the extended recovery from the Great Dying.
Researchers say the mass extinction was triggered by a series of severe volcanic eruptions in a region called the Siberian Traps. After 1 million years of heavy volcanic activity, an area larger than Europe was covered in a layer of once-molten igneous rock 1 mile to 3 miles thick.
But that alone likely wasn’t enough to kill off nearly everything and delay the eventual recovery. Researchers theorize that magma from the initial eruptions burned through an ancient coal bed. That event, in essence, unleashed hell.
Thomas Algeo, a University of Cincinnati geologist, said huge amounts of carbon dioxide and methane were released, killing off most remaining species. (Those species that survived, including dinosaurs, later grew and diversified.)
Algeo leads the team that includes Saltzman and OSU doctoral student Alexa Sedlacek. Their work is supported by the National Science Foundation.
Scientists say carbon dioxide is the main culprit behind modern climate change, trapping heat in the atmosphere. Add methane to the mix, and you have even more trouble. Methane is 20 times more effective than carbon dioxide at trapping that heat.
After the Great Dying, increases in global temperatures made life nearly impossible for plants and animals on land and heated the oceans to an average 100 degrees Fahrenheit. In the air, carbon dioxide and methane mixed with water and formed acid rain, which turned the world’s oceans acidic.
The acid rain also eroded rock and sent tons of sediment into the oceans, where it clogged gills on remaining aquatic animals and buried plants. The loss of life on land also aided the erosion, Sedlacek said.
“Because of the mass extinction on land, there were less forest ecosystems, and that left more exposed rocks for weathering,” she said.
Sedlacek and Saltzman analyzed limestone rock that formed in the oceans from those eroded sediments and turned up in a gorge in northern Iran. By measuring the amount of carbon in the rock, collaborating Austrian researchers were able to show that Earth’s climate was altered for about 5 million years after the extinction event.
Powdered rock was then sent to Saltzman and Sedlacek, who measured the ratio of two isotopes of strontium to show how much bedrock eroded from the land to the oceans. A change in that ratio indicated a rapid pace of erosion.
The findings on the ocean’s increased temperatures came from a separate study by researchers at China University of Geosciences, Wuhan, which was published recently in the journal
Science. Saltzman and Sedlacek presented their erosion findings on Nov. 4 in Charlotte, N.C., at the Geological Society of America’s annual meeting.
Saltzman said the Great Dying offers a window on the effects of climate change. He and Algeo cautioned that the current predictions for climate change are far from the global catastrophe that occurred 250 million years ago.
Algeo estimates the average temperature increase then was two to three times higher than the increase climatologists are forecasting.
Still, Saltzman said reactions to climate change can be severe.
“Life is quite sensitive to the temperature changes,” he said. “It’s pretty clear from the geologic record that the more severe the episode of global warming the more difficult it is for species to re-establish themselves.
- “To me, the lesson is if you add CO2 to the atmosphere you increase global temperatures, and this has a negative impact on the diversity of life.”