Earth Could Take 10 Million Years to Recover From Mass Extinction Caused by Humans

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File photo of a crocodile, one of the few species to survive the Cretaceous–Tertiary extinction. Getty Images

Scientists investigating the possible effects of climate change have predicted it would take 10 million years for the diversity of species on our planet to recover after a mass extinction event.

The authors of the paper published in the journal Nature Ecology and Evolution wanted to calculate how long it takes for the Earth to return to former levels of biodiversity following a mass extinction event. "Humanity is undeniably causing elevated rates of biodiversity loss through climate change, habitat destruction, invasive species introduction, and so on," the authors warned in their study.

To answer this question, paleobiologists looked to the fossil record of the tiny single-celled planktic foraminifera following the Cretaceous-Paleogene extinction event around 66 million years ago. This was the only major event in the history of our planet which unfolded faster than current climate change, and the most recent and quickest of the five major mass extinctions. Around 80 percent of animals were killed, including non-avian dinosaurs, during the Cretaceous-Paleogene mass extinction.

The team compared different species of foraminifera which existed in the 20 million years towards the end of the Cretaceous mass extinction and into the subsequent recovery period. Only after approximately 10 million years did species diversity recover.

After a mass extinction, one might expect swathes of new species to quickly appear, the authors of the study explained. But fossil records show this can happen slower than predicted. The authors surmised this is because of the way species repopulate.

Dr. Andrew Fraass co-author of the study and expert in planktic foraminifera at the University of Bristol told Newsweek: "Foraminifera are useful at the species level because of their superior fossil record, so we've been able to look at this process in a closer way than anybody else.

"From this study, it's reasonable to infer that it's going to take an extremely long time—millions of years—to recover from the extinction that we're causing through climate change and other methods."

Pointing out a limitation of the study, Fraass said the planktic foraminifera may be the best fossil record we have, but is of "one group, and a single celled one at that." It is "very very difficult" to calculate how long it would take for biodiversity to recover on a species level with the fossil records currently at scientists' disposal, he said.

"Our finding is confirming previous theoretical work, so while that's a limitation, it's hypothesized [that] it'll probably be the same for other groups as well," he said.

"It [the research] is an apt warning about the time it takes to recover from massive losses in species," said Fraass.

"We focus frequently on how long it'll take to recover from climate change (by getting CO2 back down to pre-industrial or near pre-industrial levels), which is on the scale of thousands of years, but this work corroborates it'll take millions of years for biodiversity to recover from humans."

He went on to explain: "It's a finer point whether or not we're in a mass extinction currently, as paleontological records are based on shallow marine shells and the number of families/genera that go extinct, while modern extinction is based on all organisms and species. It's a really cool question, if you're a paleontologist, but the basic answer is: if we're not currently in a mass extinction then we're close to one."

Dr. Jan Zalasiewicz, professor of palaeobiology at the University of Leicester, who was not involved in the research, told Newsweek: "The study is significant because it helps us appreciate the very long-term consequences of the striking and geologically rapid changes currently taking to the Earth's biosphere.

"The rate of recovery shown is similar to that in previous studies—of several million years—but the significance here is in its plausible explanation for this long recovery, in emphasizing the importance of the way that complex communities of organisms, that take a long time to build up, themselves create more niches to encourage greater species diversity."

Last year, a separate research paper found manmade global warming could reverse a 50-million-year-long trend of global cooling in just 200 years.

The authors of a study published in the journal Proceedings of the National Academy of Sciences warned that if greenhouse gases continued to be pumped into the Earth's atmosphere at current rates, the planet's climate would be comparable to that of the mid-Pliocene era of 3 million years ago by 2030. And by 2150 it would go back to the climate of the Eocene period, 50 million years ago.

This article has been updated with comment from Professor Jan Zalasiewicz​.