Link Found Between Ancient Climate Change and Mass Extinction

Rock strata on Anticosti Island, Quebec, Canada, one of the sites from which the researchers collected fossils.

New research led by researchers at the California Institute of Technology, Caltech, have discovered new details that support the idea that the mass extinction that took place approximately 450 million years ago, known as the Late Ordovician mass extinction, was linked to a cooling climate.

During the Late Ordovician mass extinction more than 75 percent of marine species died, but left very little evidence to help us understand how or what happened.

“While it’s been known for a long time that the mass extinction is intimately tied to climate change, the precise mechanism is unclear,” says Seth Finnegan, a postdoctoral researcher at Caltech, and lead author of the paper which was published on the online version of the journal Science.

The Late Ordovician mass extinction took place at the same time as a glacial period, which saw temperatures cool worldwide, and glaciers spread and increase in number. North America was sitting on the equator and the remaining continents were all clumped together into a supercontinent now known as Gondwana, which stretched from the equator to the South Pole.

Previous methods have been unhelpful in uncovering relevant information about what happened and how so many species were lost, but a new method developed in the laboratory of John Eiler, Sharp Professor of Geology and professor of geochemistry at Caltech, the researchers have been able to determine the average temperatures during the Late Ordovician period.

“By providing independent information on ocean temperature, this new method allows us to know the isotopic composition of 450-million-year-old seawater,” Finnegan says. “Using that information, we can estimate the size of continental ice sheets through this glaciation.”

Given clearer information of how much ice there was at the time of the mass extinction, the researchers have been able to learn more about what might have caused the extinction.

“We have found that elevated rates of climate change coincided with the mass extinction,” says Aradhna Tripati, a coauthor from UCLA and visiting researcher in geochemistry at Caltech.

During the period studied, tropical ocean temperatures were higher than they are now, even though moderately sized glaciers still existed near the poles prior to and following the mass extinction event. But during the period of time in which the extinction event is believed to have taken place, glaciation peaked, tropical surface waters cooled by five degrees, and the ice sheets on Gondwana grew to be as large as 150 million cubic kilometres, a size larger than the glaciers that covered Antarctica and most of the Northern Hemisphere during the modern era’s last ice age, some 20,000 years ago.

“Our study strengthens the case for a direct link between climate change and extinction,” Finnegan says. “Although polar glaciers existed for several million years, they only caused cooling of the tropical oceans during the short interval that coincides with the main pulse of mass extinction.”

Source: California Institute of Technology
Image Source: Woody Fischer

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