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How Earth Recovered from an Earlier Extinction


How long might it take to recover from the Sixth Great Extinction that scientists tell us is now underway?

The most well known extinction event was the one that brought an end to the reign of the dinosaurs 65 million years ago. That was the Fifth Great Extinction. But much larger than that was the Fourth Great Extinction, 250 million years ago.

And it took 10 million years before life had stabilized again – albeit with very different species from what went before.

Ten million years is a long time. Ten million years ago, grasslands and savannahs were taking shape around the world, horses were evolving from their mini form, and the very earliest pre-human hominids were still four million years in the future.

In that Fourth Great Extinction, only 10 percent of plant and animal species survived. And now, a new study suggests that the damage was so serious that life took a very long time to reestablish itself. There were also continuing after-effects of the extinction event itself.

“The causes of the killing — global warming, acid rain, ocean acidification — sound eerily familiar to us today.”

Whereas the Fifth Extinction appears to have been caused by an asteroid impact, the Fourth Extinction was basically a global warming event, more carbon in the atmosphere, a lack of oxygen in the oceans, ocean acidification and acid rain.

No one is suggesting that those same factors are at work to the same extent today, but yes, today’s climate change includes all those factors.

“Life seemed to be getting back to normal when another crisis hit and set it back again,” said Professor Michael Benton from the University of Bristol. “The carbon crises were repeated many times, and then finally conditions became normal again after five million years or so.”

After that, new animals began to emerge. Some of them were the ancestors of crabs and lobsters. Then the first marine reptiles appeared. They were the the basis of future ecosystems, and would give rise to the dinosaurs.

This vast multi-million-year event re-set the whole evolution of life on Earth. Likewise, the demise of the dinosaurs, as a result of the next major extinction event, led to the rise of the mammals, including, most recently, us humans.

Now a Sixth Great Extinction is underway – the first of the six to have been brought about by a single species.

“The causes of the killing — global warming, acid rain, ocean acidification — sound eerily familiar to us today,” said Dr. Benton. “Perhaps we can learn something from these ancient events.”

The study is published in Nature Geoscience.