‘Great dying’ on Earth could happen again, study says
More than two-thirds of life on Earth died off some 252 million years ago, in the largest mass extinction event in Earth’s history.
Researchers have long suspected that volcanic eruptions triggered “the Great Dying,” as the end of the Permian geologic period is sometimes called, but exactly how so many creatures died has been something of a mystery.
Now scientists at the University of Washington and Stanford believe their models reveal how so many animals were killed, and they see frightening parallels in the path our planet is on today.
Models of the effects of volcanic greenhouse gas releases showed the Earth warming dramatically and oxygen disappearing from its oceans, leaving many marine animals unable to breathe, according to a study published Thursday in the peer-reviewed journal Science. By the time temperatures peaked, about 80 per cent of the oceans’ oxygen, on average, had been depleted. Most marine animals went extinct.
The researchers tested the model’s results against fossil-record patterns from the time of extinction and found they correlated closely. Although other factors, such as ocean acidification, might have contributed some to the Permian extinction, warming and oxygen loss account for the pattern of the dying, according to the research.
By this century’s end, if emissions continue at their current pace, humans will have warmed the ocean about 20 per cent as much as during the extinction event, the researchers say. By 2300, that figure could be as high as 50 per cent.
“The ultimate, driving change that led to the mass extinction is the same driving change that humans are doing today, which is injecting greenhouse gases into the atmosphere,” said Justin Penn, a UW doctoral student in oceanography and the study’s lead author.
Curtis Deutsch, a UW associate professor of oceanography and an author of the research, said if society continues to pump greenhouse gases at our current rate, “we have no reason to think it wouldn’t cause a similar type of extinction.”
The Earth 252 million years ago was a much different place. The continents as we know them today were still mostly one land mass, named Pangea, which looks like a chunky letter “C” on a map.
The climate, however, resembled Earth’s now, and researchers believe animals would have adapted many traits, like metabolism, that were similar to creatures today. Nearly every part of the Permian Ocean, before the extinction, was filled with sea life.
“Less than one per cent of the Permian Ocean was a dead zone — quite similar to today’s ocean,” Deutsch said.
The series of volcanic events in Siberia that many scientists believe set off the mass extinction “makes super volcanoes look like the head of a pin,” said Seth Burgess, a geologist and volcanologist with the United States Geological Survey.
“We’re talking about enough lava erupted onto the surface and intruded into the crust to cover the area of the United States that if you looked at the U.S. from above was maybe a kilometre deep in lava,” he said.
Burgess, who has researched the Siberian Traps volcanic events but did not work on the new Science paper, said scientists believe magma rising from the earth released some extinction-causing greenhouse gases.
In addition, sills of magma still inside the earth heated massive deposits of coal, peat and carbonate minerals, among others, which vented even more carbon and methane into the atmosphere.
“That’s how you drive the Permian mass extinction, by intruding massive volumes of magma into a basin rich in carbon-bearing sediments,” he said.
The UW and Stanford research “takes the next step in figuring out why things died at the end of the Permian,” Burgess said. “It couples what we think was happening in the climate with the fossil record, and it does it elegantly.”
It took a supercomputer more than six months to simulate all the changes the volcanic eruptions are suspected of causing during the Permian period. The computer models go into remarkable detail — simulating things such as clouds, ocean currents and marine plant life — in describing what temperatures and conditions were like on Earth.