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The demise of the dinosaurs 65 million years ago is the best known.

But the most extreme extinction event occurred about 185 million years before that.The Permian-Triassic extinction event – often called The Great Dying – killed off 70% of all land animal species and an incredible 96% of all marine species.Because The Great Dying happened 250 million years ago, any evidence for its exact cause is long-buried. The best theory, though, points to a long series of volcanic eruptions that released a lot of carbon-dioxide into the atmosphere.

(Image: Getty)

(Image: Getty)

Now it looks as if we are headed for another one of these cataclysms. And, like the Permian-Triassic extinction, CO2 is the most likely cause.MIT geophysics professor Daniel Rothman released new data this week showing that rising CO2 levels in the Earth’s oceans are approaching an irrevocable tipping point.He created a computer model that simulated dumping a large amount of carbon dioxide in oceans. He discovered that finding that when the gas was added to a normal marine environment, the negative effects were short-lived.But when he altered the experiment to simulate the effects of continuously dumping CO2 into an already carbon-compromised ocean the effects were dangerous and unpredictable.

(Image: Getty)

His ocean model soon reached a tipping point where "a cascade of chemical feedbacks” caused a new Great Dying.Since the dawn of the Industrial Revolution, that is exactly what we have been doing. Rothman believes that we are close to the tipping point where the carbon build-up is irreversible. And the previous two times that levels have been this high were at the beginning of two of the most devastating mass extinctions – including The Great Dying."Once we're over the threshold, how we got there may not matter," Rothman told MIT News. "Once you get over it, you're dealing with how the Earth works, and it goes on its own ride."

(Image: Getty)

Other scientists said the study, which will be published this week in the Proceedings of the National Academy of Sciences, represents a clear call for immediate action to drastically reduce the amount of carbon that is being pumped into the world's oceans. Climate action groups and grassroots movements have long called on governments to impose a moratorium on fossil fuel drilling, which pumps about a billion metric tons of carbon into the atmosphere every year.Timothy Lenton, a professor of climate change and earth systems science at the University of Exeter, told Common Dreams: ”We already know that our CO2-emitting actions will have consequences for many millennia,"This study suggests those consequences could be much more dramatic than previously expected.""If we push the Earth system too far," Lenton added, "then it takes over and determines its own response—past that point there will be little we can do about it."