How Apocalypses Paved the Way for Humans (and terror birds) | Nat Geo Explores

Everybody thinks mass extinctions are a bad thing, and for some, yeah, they were literally the worst. But they also show how nature can bounce back. In fact, while extinctions are like a large scale delete button, they're also a way to trigger some new amazing life.

There's been a lot of speculation about the evolutionary role of mass extinctions, and I think mass extinctions have been really important. I think they play a really major role in opening up ecological opportunities for lineages to diversify and knocking back lineages that have been dominant for long periods of time.

The really big mass extinctions are the ones that show up very dramatically in the fossil record, and those are fondly called the big five. The big five mass extinctions are scattered through the history of life over the last 550 million years, and what caused them were things like massive volcanic eruptions, climate changes, and even apocalyptic asteroids.

The big five accounted for 50% and by some estimates up to 90% loss of all the species. I think these mass extinctions are important evolutionary agents that help shake the system loose. Because they open up large amounts of ecological space, they probably do allow for greater evolutionary inventiveness than might have been potentially possible in a situation of a really crowded world.

Mass extinctions basically cleared the decks and made room for new life. But it didn't happen overnight; we are talking tens of millions of years before we saw life start to make a comeback. But eventually, after this one happened, lots of new fish came to be, and here both plants and reptiles really diversified. Then the first mammals and dinosaurs appeared.

Then, after this, tons more dinosaur species emerged. After the mass extinction that killed off the dinosaurs, there was a new sheriff in town: terror birds. There's a whole lineage of large carnivorous birds that diversified after the dinosaurs went extinct through the Cenozoic. Some were just two or three feet tall; some of them were six or seven feet tall. Those would be pretty spectacular running around the landscape, chasing down their mammalian prey.

I think luckily for us, they're gone! So, dead dinosaurs meant new life for them, and eventually, new life for us. Okay, but seriously, how did anything survive?

One of the rules that we find looking at every single mass extinction, and many other extinction events besides, is that species that are widespread geographically preferentially survive the mass extinction. Species that are spatially restricted, just in one little area, those preferentially go extinct. What it says to me is that what really mattered was having your evolutionary eggs in many different geographical baskets.

So what could this mean for humans and future mass extinctions? We don't really know what sort of seal activities are ahead for the kinds of pressures that we're bringing to bear on the ecosystem today. Humans will almost certainly survive in some way; that's because humans have spread nearly everywhere.

Really, more the question is the quality of life of those humans and who else will be left behind to occupy the planet with us. That's really an interesting question. There are plenty of species that we rely on, either directly or indirectly, that might fall into the high extinction risk category.

So understanding mass extinctions and how species recovered can help us a lot today. There are some fundamental rules about how the world works under stress that we can, in fact, adopt and use to our advantage to understand what's taking place and something about what's going to happen next.