How Does Life Recover from Mass Extinctions?

Every few dozen million years there’s a devastating event on Earth that kills nearly all the living creatures on our planet. Dr. Michael Habib explains how life always finds a way of recovering.

“Hello, my name is Michael Habib, and I’m an assistant professor of Cell and Neurobiology at the University of Southern California. I’m a biomechanist and paleontologist.”

How does life survive a mass extinction?
“One of the most amazing things about life on earth is that if you don’t kill EVERYTHING, it will eventually recover. Extinction is forever – if you kill a group, you’ll never have that group again, but what we find is that often the same ecologies show up again after a major extinction, because other groups end up diversifying to do the same things as groups we’d seen elsewhere.”

“So the world doesn’t end up looking entirely different after a mass extinction, although it would be quite different in a lot of ways. And even the great End Permian extinction killed about 99 percent of all species, or at least all the ones we can measure in the fossil record, and left that one percent, that’s all it takes to eventually recover.”

“Now, I imagine if you took a time machine to the first six months of the Triassic, it would be a very lonely, kinda ugly world. You’d notice that animals and plants were missing. The massive extinction affected all sorts of organisms.But, at the scales we’re looking at in the geologic record – tens of millions of years, a time span that’s pretty much unfathomable to human experience, you can eventually recover that diversity, with speciation event after speciation event kicks in and eventually creates a new diversity.”

“But after each mass extinction event, the world looks a bit different. You know, if I were to drop you in a time machine before the End Permian extinction, you’d notice a lot of things different about the world. You’d notice strange large mammal-like reptiles with large saber teeth running around as the large terrestrial organisms. You would see a few of the major groups of vertebrates that exist today, especially marine, but a lot of the terrestrial groups would be very different.”

“If I jump to after the End Permian extinction, enough that life had recovered, you’ll see those ancestors to dinosaurs, those terrasaurs, would show up in the mid to late Triassic. Then you start to see some plant groups that look more familiar to us, like plants that look a little bit more like modern conifers, things like that. So the world would definitely look different, but life does go on.”

When Everything On Earth Died

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Hey, remember that one time when 90% of all life on Earth got wiped out?

I don’t either. But it’s a good thing it happened because otherwise none of us would be here to… not remember it. Still, the end-Permian Extinction — a.k.a. the Great Dying — was very much a real crisis for life on Earth 252 million years ago. It makes the K-T extinction event of the dinosaurs look like a rather nice day by comparison, and is literally the most catastrophic event known to have ever befallen Earthly life. Luckily for us (and pretty much all of the species that have arisen since) the situation eventually sorted itself out. But how long did that take?

An alien Earth: what our planet looked like during the time of the Permian Extinction. (Via The Planetary Habitability Laboratory @ UPR Arecibo, NASA, Ron Blakey and Colorado Plateau Geosystems, Inc., and The PaleoMap Project)

The Permian Extinction was a perfect storm of geological events that resulted in the disappearance of over 90% of life on Earth — both on land and in the oceans. (Or ocean, as I should say, since at that time the land mass of Earth had gathered into one enormous continent — called Pangaea — and thus there was one ocean, referred to as Panthalassa.) A combination of increased volcanism, global warming, acid rain, ocean acidification and anoxia, and the loss of shallow sea habitats (due to the single large continent) set up a series of extinctions that nearly wiped our planet’s biological slate clean.

Exactly why the event occurred and how Earth returned to a state in which live could once again thrive is still debated by scientists, but it’s now been estimated that the recovery process took about 10 million years.

(Read: Recovering From a Mass Extinction is Slow Going)

Research by Dr. Zhong-Qiang Chen from the China University of Geosciences in Wuhan, and Professor Michael Benton from the University of Bristol, UK, show that repeated setbacks in conditions on Earth continued for 5 to 6 million years after the initial wave of extinctions. It appears that every time life would begin to recover within an ecological niche, another wave of environmental calamities would break.

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

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

– Michael Benton, Professor of Vertebrate Palaeontology at the University of Bristol

It wasn’t until the severity of the crises abated that life could gradually begin reclaiming and rebuilding Earth’s ecosystems. New forms of life appeared, taking advantage of open niches to grab a foothold in a new world. It was then that many of the ecosystems we see today made their start, and opened the door for the rise of Earth’s most famous prehistoric critters: the dinosaurs.

“The event had re-set evolution,” said Benton. “However, the causes of the killing – global warming, acid rain, ocean acidification – sound eerily familiar to us today. Perhaps we can learn something from these ancient events.”

The team’s research was published in the May 27 issue of Nature Geoscience. Read more on the University of Bristol’s website here.