Earth has already witnessed five mass extinctions -- devastating events that wipe out the majority of life on the planet. The Cretaceous-Tertiary extinction event (known as the K/T extinction, for short), was likely caused by an asteroid colliding with Earth, and caused the dinosaurs to disappear. A more distant extinction event, "The Great Dying," was likely caused by a volcanic event.
Now, we are likely at the brink of a sixth mass extinction. By 2070, the majority of coral reefs on Earth could vanish, killing 25 percent of all fish species in the process. Earth's wildlife population has decreased by 50 percent in the last 40 years alone. With a drastically changing climate already taking its toll on our environment, we can expect to see many more changes like these in the near future.
Salon spoke with evolutionary biologist and host of the documentary "Mass Extinction: Life at the Brink," Sean B. Carroll to learn more about our (possibly) impending doom.
This interview has been lightly edited.
What exactly is a mass extinction?
Well, there are some definitions out there, but let's just say that when the majority of species on the planet disappear in a relatively short period of time. Here comes the parentheses part ... Some define it as 75 percent but it's very hard to know what 75 percent of life on Earth is at a given time. You know, just because of the sparsity of the fossil record and things like that. You can ask me more technically. But so let's just say it's the majority and they stand out against sort of the background pattern of extinction. So, if you just plot the known diversity of life on the planet at any given time there are these pretty dramatic drops and they've been known for a long time in the rock record, because it turns out they coincide with pretty dramatic changes in the rocks themselves. So, you can sort of see from the rock record that something's happened on the planet and it turns out that those tend to be boundaries where there's a pretty dramatic change between life before and life after that phase in time. Geologists have been naming rocks for a long time. This goes back a couple of centuries and it just turns out that the boundaries between the big phases of time often are boundaries between eras of life marked by the extinction of the previous era and in the appearance of new kinds of things.
There's the long answer, but the short one is it's when most of the species on the planet disappear in a pretty quick period of time.
You are an evolutionary biologist, not a paleontologist -- how did you get involved with the documentary?
There's two parts to that. So, yes, I'm an evolutionary biologist and so for someone interested in the history of life on the planet, mass extinctions are an incredible mystery; you know, what could happen that would make life disappear in such a dramatic way? The second reason I got involved is that for the last 10 or 12 years, I've spent a lot of time communicating science to the public in the forms of books, public speaking, participation in documentaries, and then in the last four years I'm the head of science education at HHMI [Howard Hughes Medical Institute], which is a large private funder of science education. And one thing we did here was start a filmmaking unit and this is one of the films that that unit has made. And one of my contributions was to go around the world a bit and help colleagues who actually work in the area of extinction tell those stories.
Seems like a great gig to have!
Well, you want an honest answer to that one? Most days it is. This gig, in terms of, you saw where I got to go, Italy, Spain, the Badlands, Texas. Yeah, that was okie-dokie.
In the documentary, you call mass extinction the greatest murder mystery. Will you say a little more about both your experience and the experience of the primary investigators studying the topic and attempting to piece together what may have happened in these extinction events?
They are murder mysteries in the same way that you are kind of working from forensic evidence and you have a bunch of possible suspects. For many many decades, geologists and biologists were trying to imagine suspects -- and that was anything from, you know, supernovas in outer space to gas bubbles bubbling up in the ocean to also maybe some creatures, like, eating themselves to death or exhausting all the resources on the planet and things like this. So the question is where do the forensic clues lead you.
I think what is particularly cool about the two mass extinctions in this film is that right at these rock boundaries where there's a dramatic change in life, there's a chemical signature there that geologists discovered. In the case of the K/T extinction, it was that iridium spike -- a rare chemical not normally found out on the crust of the earth. And then in the case of the end-Permian [the Great Dying], it's this big spike in carbon, which is coming from carbon dioxide. So those are almost sort of the calling cards of the culprits here in the murder mystery. The geologists had to piece together all sorts of evidence. And I don't think it's corny to call it a mystery because there's this element of trying to find out, you know, what sort of calling card was left behind? What signature was there? What could possibly cause those things, iridium or carbon spikes or whatever? And then to look around the world and see whether or not the same signature was found in different places.
Then finally there's this timing aspect, which is, you know, if we see this change here, does animal and plant life change in step at the same time? In the case of the end-Permian, trying to find parts of the world that both revealed the extinction as you saw in China and timing what happened in Siberia, that's quite a technical challenge. That's the case of finding whether or not two events coincide in time which is very much like a Sherlock Holmes.
I'm sort of hoping that viewers can understand just, in fact, how much like detective work science is. Following clues, playing hunches, being surprised, having to explain new evidence that you might not have had room for before. But this is a pretty amazing global and multidisciplinary effort to pin down all these things and to ask, OK, if an asteroid did hit the Earth, how did that kill everything or kill so much? And if volcanism in Siberia was going on, then why was that so devastating? And that's where we felt justified in putting the two extinctions together in the same film because it doesn't matter whether the triggers are different, the idea is the same. You have really rapid environmental change on a global scale, right? Huge change on a global scale very quickly, that's what's going on and you realize that you know just, organisms aren't equipped to deal with that scale of change.
There's a short answer for you.
What does it take to wipe out most of life on the planet? You said an extreme environmental event.
Yes, large, rapid, global change. That's it. It's large in magnitude, so it's not just a little bump, it's a big change. Very rapid over time. Obviously, something like the asteroid impact was almost instantaneous and then global, so if you just have a little regional event that's not going to give you a mass extinction across the world. But because the K/T impact was so huge and blew so much stuff outside the atmosphere that fell back to Earth around the globe, it had a global effect. It affected the oceans as well as the land. And in the end-Permian, so much climate changing gas was pumped into the atmosphere, that of course circulates across the globe, affecting both land and ocean. So that picture of what to take is really pumping stuff up into the atmosphere and into the oceans that will circulate across the globe. That should sound very familiar to current headlines and there's no accident there.
Are we on the brink of a sixth mass extinction?
Yeah, and [University of California, Berkeley, paleontologist] Tony Barnosky is asked that question sort of directly in the film and he's an expert, a world-recognized expert working on the question. To answer for him, he would say if we do business as usual, that's a certainty. Since, say, 1800, with the Industrial Revolution and the way we have fished the oceans, timbered the forests, developed the land and basically removed creatures simply through conflict or hunting or harvesting — that's the path we're on.
And it's not a faraway sort of thing, because what we've come to now -- and I think this is awfully hard to get this across in 50 minutes but that's what we tried -- is that what's happened is that, I mean there's sort of good news and bad news. Tony will say that only about 1 percent of the species at risk have gone extinct and so we do have a chance to halt or restore things. They're not gone. On the other hand, the populations are much smaller than they used to be in history. So ranges of creatures are really reduced and their population sizes are really reduced so they're very vulnerable to the next insult.
Grizzlies used to roam huge swaths of North America. It's nice that Grizzlies have rebounded in Yellowstone from about 150 to 600, but that's still a minuscule population and that's not a big resource in terms of the coming centuries, so that's just an example. There's only 3,000 tigers left in the world ,and you know that some of the rhinos are down to incredibly tiny populations, so those are just examples. There's thousands and thousands of species at risk.
So the answer is yes, if we continue at the pace we've been going, which has been a breakneck pace of utilizing Earth's resources as human populations have exploded. But the good news is they're not extinct, so there's room here for rebound. Which may not have been your question, but it's part of the answer.
How do we facilitate that rebound? What do we do to prevent an extinction event?
I think that's a great and really tough question. I only have a little starter answer and it's in the film: For now, I think we have to buy time. In other words, buy time before we sort of globally conduct business differently. You know, part of the answers are renewable energy and things like this and actually some kind of slowing of the human population growth, but that's a very very difficult thing to manage politically -- the haves and the have nots. I don't underestimate how difficult that is. What is doable, what is actionable is to strengthen, if not expand the reserves we already have. So something like 15 percent of land has been set aside as reserves, that's actually up from I think about 12 percent ... But there was just a worldwide convention on parks in Sydney [the World Parks Congress] just like a week and a half or two weeks ago and that's one of the press releases I think I saw out of the convention. And then there's some percentage, I can't remember the exact number, of marine reserves [much less -- the goal for 2020 is 10 percent protected land]. So these are especially effective when they've been established in places with high diversity and like in marine reserves where they are really important nurseries for fish, they have an effect far beyond their borders.
These are really important things. And those things are sort of decided at a local level. Let's not wait for 160 countries to agree on something; let's act where people are both willing and able to do something. That's reserve by reserve, place by place across the world. There's some great stories in that arena where especially in parts of the world where people have come to appreciate that things being left intact and alive are more valuable than their being harvested, say, as fisheries. And as for tourism and things like that, and there are a lot of places in the world where tourism ranks right up there with agriculture as a major economic source. So there can be economic incentives, strong economic incentives, to really preserve what we've got and that's sort of, you know, a country by country and region by region situation.
It's not hopeless. Whether that's just my psychology of refusing to believe it is hopeless. People need something to look at and there are people working very hard and with important success in doing this sort of thing, and the messages that people get that are of doom and dysfunction, that's why I talk about looking locally ...
I could just tell you, you didn't ask me but just volunteering that, you might say why make a film? Obviously, this is more to get the conversation started than just to watch a film. So I think over the next years I also wanted people to understand that even without climate change, we'd have an extinction crisis from the last couple hundred years of population growth and industrial activity, right? The loss of habitat and that sort of thing. Climate change just is now adding one big variable, one big uncertainty on top of an already pretty strained situation. That's one reason in the film I wanted people to appreciate that the loss of habitat and things like that sort of all add up. I think people are a bit burned out on just hearing the climate change refrain. It's just become one of those topics that, of course, you know there's two camps and they're just shouting at each other.
There was a report just around two or three weeks ago from the World Wildlife Fund, I think it was, based on data from the International Union for the Conservation of Nature, that the populations of wildlife across the globe have declined by more than 50 percent in the last 40 years. So that means if you just added up all the animals in the world 40 years ago, there's half as many now. And I'm old enough that that happened on my watch. That's upsetting. We don't want to see that go by another half, or worse. We know that in just sheer numbers, populations are really, really reduced and I just hope people can start talking about that and not getting sort of hung up on the buzzwords, and realizing through a combination of factors, things are disappearing and some of those things are going to really impact human lives in an important way. Other things may just be sort of canaries in the coal mine but nonetheless, they are telling us something.
"Mass Extinction: Life at the Brink" will air on Nov. 30 at 8 p.m. ET on the Smithsonian Channel.