The Two Great Killers of 'The Great Dying'

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The Siberian Traps in northern Russia are picturesque. The expansive region is graced with serene slopes that jut into striking plateaus. Hiding behind this beauty, however, is a calamitous history, revealed by the basalt rock that underlies the region. Roughly 250 million-years-ago, the Siberian Traps exploded in a series of volcanic eruptions that continued off and on for two million years. When the upheaval finally concluded, 770,000 square miles of magma covered the land and an enormous amount of climate-altering gases had entered the atmosphere. As best scientists can tell, the global changes triggered by these gases resulted in the Permian–Triassic extinction event, "The Great Dying," in which up to 96% of marine species and 70% of terrestrial vertebrate species disappeared. It was the worst mass extinction event in Earth's history.

Now, in a new paper published to the journal Science, scientists from the University of Washington and Stanford University have zeroed in on the two simple changes in the ocean that drove so many species to extinction: less oxygen and more heat. 

Simulating the global warming that occurred (as validated by geochemical data) during the Permian–Triassic extinction within a model of Earth's climate, the researchers found that oxygen available in seawater to marine species would have fallen by 76 percent. That's because hot water can't hold as much dissolved oxygen. At the same time, ocean temperatures skyrocketed, potentially reaching a steamy 104 degrees Fahrenheit in some locations, thus increasing organisms' metabolic demands. As overheated marine life was desperate for more life-giving oxygen, there was less and less for them to breath. The suffocating strain killed indiscriminately, littering the seafloor with future fossils. Only species already adapted to warmer, tropical waters stood a chance.

Could this calamitous scenario play out again given the current rate of ocean warming? Using publicly available IPCC data, the researchers estimated that by 2300, the oceans could warm to levels roughly ~35 to 50% of those required to account for most of the end-Permian extinctions. We may be on our way to a "Great Dying" sequel.

Source: Justin L. Penn, Curtis Deutsch, Jonathan L. Payne, Erik A. Sperling. "Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction." Science. 7 Dec. 2018.

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