Earth Is Not in the Midst of a Sixth Mass Extinction

At the annual meeting of the Geological Society of America, Smithsonian paleontologist Doug Erwin took the podium to address a ballroom full of geologists on the dynamics of mass extinctions and power grid failures—which, he claimed, unfold in the same way.

“These are images from the NOAA website of the US blackout in 2003,” he said, pulling up a nighttime satellite picture of the glowing northeastern megalopolis, megawatts afire under the cold dark of space. “This is 20 hours before the blackout. You can see Long Island and New York City.”

“And this is seven hours into the blackout,” he said, pulling up a new map, cloaked in darkness. “New York City is almost dark. The blackout extended all the way up into Toronto, all the way out to Michigan and Ohio. It covered a huge section of both Canada and the United States. And it was largely due to a software bug in a control room in Ohio.”

Erwin is one of the world’s experts on the End-Permian mass extinction, an unthinkable volcanic nightmare that nearly ended life on earth 252 million years ago. He proposed that earth’s great mass extinctions might unfold like these power grid failures: most of the losses may come, not from the initial shock—software glitches in the case of power grid failures, and asteroids and volcanoes in the case of ancient mass extinctions—but from the secondary cascade of failures that follow. These are devastating chain reactions that no one understands. Erwin thinks that most mass extinctions in earth’s history—global die-offs that killed the majority of animal life on earth—ultimately resulted, not from external shocks, but from the internal dynamics of food webs that faltered and failed catastrophically in unexpected ways, just as the darkening eastern seaboard did in 2003.

“Because it was not clear how to manage that collapse—although after the fact it was clear that it should have been easily contained—it cascaded into failure of grids across the northeastern United States ...  I mention this because it turns out that, from a mathematical point of view, the problem of understanding these food webs is exactly the [same] problem as understanding the nature of the power grid. There’s a very rapid collapse of the ecosystem during these mass extinctions,” he said.

I had written to Erwin to get his take on the contemporary idea that there is currently a sixth mass extinction under way on our planet on par with the so-called Big Five mass extinctions in the history of animal life. Many popular science articles take this as a given, and indeed, there’s something emotionally satisfying about the idea that humans’ hubris and shortsightedness are so profound that we’re bringing down the whole planet with us.

Given how severely humans have damaged the natural world over the millennia, it was an idea I found attractive, and it’s one even shared by many geologists and paleontologists. Our destruction is so familiar—so synonymous with civilization—in fact, that we tend to overlook how strange the world that we’ve made has become. For instance, it stands to reason that, until very recently, all vertebrate life on the planet was wildlife. But astoundingly, today wildlife accounts for only 3 percent of earth’s land animals; human beings, our livestock, and our pets take up the remaining 97 percent of the biomass. This Frankenstein biosphere is due both to the explosion of industrial agriculture and to a hollowing out of wildlife itself, which has decreased in abundance by as much as 50 percent since 1970. This cull is from both direct hunting and global-scale habitat destruction: almost half of the earth’s land has been converted to farmland.

The oceans have endured a similar transformation in only the past few decades as the industrial might developed during World War II has been trained on the seas. Each year fishing trawlers plow an area of seafloor twice the size of the continental United States, obliterating the benthos. Gardens of corals and sponges hosting colorful sea life are reduced to furrowed, lifeless plains. What these trawlers have to show for all this destruction is the removal of up to 90 percent of all large ocean predators since 1950, including familiar staples of the dinner plate like cod, halibut, grouper, tuna, swordfish, marlin, and sharks. As just one slice of that devastation, 270,000 sharks are killed every single day, mostly for their tasteless fins, which end up as status symbol garnishes in the bowls of Chinese corporate power lunches. And today, even as fishing pressure is escalating, even as the number of fishing boats increases, even as industrial trawlers abandon their exhausted traditional fishing grounds to chase down ever more remote fish stocks with ever more sophisticated fish-finding technology, global fish catch is flatlining.

Closer to shore, coral reefs, the wellspring of the ocean’s biodiversity, have declined in extent by as much as a third since only the 1980s. These paradises are plagued by overfishing, pollution, and invaders, but 500 million people, many of them poor and living in the developing world, rely on them for food, storm protection, and jobs. As in the handful of reef collapses of the geological past, modern reefs are expected to collapse from warming and ocean acidification by the end of the century, and possibly much sooner. During record-breaking temperatures in 1997–1998, 15 percent of the world’s reefs died. In the past few months a similar wave of death struck the Great Barrier Reef. It won’t be the last.

So things don’t look so good, no matter where we look. Yes, the victims in the animal world include scary apex predators that pose obvious threats to humans, like lions, whose numbers have dropped from 1 million at the time of Jesus to 450,000 in the 1940s to 20,000 today—a decline of 98 percent. But also included have been unexpected victims, like butterflies and moths, which have declined in abundance by 35 percent since the 1970s.

Like all extinction events, so far this one has been phased and complex, spanning tens of thousands of years and starting when our kind left Africa. Other mass extinctions buried deep in earth’s history have similarly played out over tens of thousands, even hundreds of thousands of years. To future geologists, then, the huge wave of extinctions a few thousand years ago as First Peoples spread out into new continents and remote archipelagoes will be all but indistinguishable from the current wave of destruction loosed by modernity and its growing appetites. Surely we’ve earned our place in the pantheon next to the greatest ecological catastrophes of all time: the so-called Big Five mass extinctions of earth history. Surely our Anthropocene extinction can confidently take its place next to the juggernauts of deep time—the Ordovician, Devonian, Permian, Triassic and Cretaceous extinctions.

Erwin says no. He thinks it’s junk science.

“Many of those making facile comparisons between the current situation and past mass extinctions don’t have a clue about the difference in the nature of the data, much less how truly awful the mass extinctions recorded in the marine fossil record actually were,” he wrote me in an email. “It is absolutely critical to recognize that I am NOT claiming that humans haven’t done great damage to marine and terrestrial [ecosystems], nor that many extinctions have not occurred and more will certainly occur in the near future. But I do think that as scientists we have a responsibility to be accurate about such comparisons.”

I had a chance to sit down with Erwin after his talk at the annual geology conference. My first question—about a rumor I had heard from one of his colleagues that Erwin had served as a sort of mass extinction consultant to Cormac McCarthy while the notoriously secretive author was constructing the post-apocalyptic world of The Road—Erwin coyly evaded. But on the speculative sixth mass extinction, he was more forthcoming.

“If we’re really in a mass extinction—if we’re in the [End- Permian mass extinction 252 million years ago]—go get a case of scotch,” he said.

If his power-grid analogy is correct, then trying to stop a mass extinction after it’s started would be a little like calling for a building’s preservation while it’s imploding.

“People who claim we’re in the sixth mass extinction don’t understand enough about mass extinctions to understand the logical flaw in their argument,” he said. “To a certain extent they’re claiming it as a way of frightening people into action, when in fact, if it’s actually true we’re in a sixth mass extinction, then there’s no point in conservation biology.”

This is because by the time a mass extinction starts, the world would already be over.

“So if we really are in the middle of a mass extinction,” I started, “it wouldn’t be a matter of saving tigers and elephants—”

“Right, you probably have to worry about saving coyotes and rats.

“It’s a network collapse problem,” he said. “Just like power grids. Network dynamics research has been getting a ton of money from DARPA [Defense Advanced Research Projects Agency]. They’re all physicists studying it, who don’t care about power grids or ecosystems, they care about math. So the secret about power grids is that nobody actually knows how they work. And it’s exactly the same problem you have in ecosystems.

“I think that if we keep things up long enough, we’ll get to a mass extinction, but we’re not in a mass extinction yet, and I think that’s an optimistic discovery because that means we actually have time to avoid Armageddon,” he said.

Erwin’s other point, that the magnitude of the Big Five mass extinctions in earth’s past dwarfs humanity’s destruction thus far, is a subtle one. He’s not trying to downplay the tremendous destruction wrought by humans, but reminding us that claims about mass extinctions are inevitably claims about paleontology and the fossil record.

“So there are estimates of what the standing crop of passenger pigeons was in the 19th century,” said Erwin. “It’s like 5 billion. They would black out the sky.”

Passenger pigeons all but serve as the mascot of the “sixth mass extinction,” their extirpation an ecological tragedy on a massive scale, and proof that humans are a geologically destructive force to be reckoned with.

“So then you ask: in a non-archaeological context, how many fossil passenger pigeons are there? How many records are there of fossil passenger pigeons?”

“Not many?” I offered.
 “Two,” he said.
“So here’s an incredibly abundant bird that we wiped out. But if you look in the fossil record, you wouldn’t even know that they were there.”

Erwin likes to recall a talk he once went to by an ecologist who had documented the troubling losses he had seen over his career in high-altitude rainforests.

“He was using this as an example of the destruction of plants in these cloud forests in Venezuela, all of which could be completely true,” Erwin said. “The problem is, the probability of finding one of those cloud forests in the fossil record is zero.”

The fossil record is incredibly incomplete. One rough estimate holds that we’ve only ever found a tantalizing 0.01 percent of all the species that have ever existed. Most of the animals in the fossil record are marine invertebrates, like brachiopods and bivalves, of the sort that are both geologically widespread and durably skeletonized. In fact, though this book (for narrative purposes) has mostly focused on the charismatic animals taken out by mass extinctions, the only reason we know about mass extinctions in the first place is from the record of this incredibly abundant, durable, and diverse world of marine invertebrates, not the big, charismatic, and rare stuff like dinosaurs.

“So you can ask, ‘Okay, well, how many geographically widespread, abundant, durably skeletonized marine taxa have gone extinct thus far?’ And the answer is, pretty close to zero,” Erwin pointed out. In fact, of the best-assessed groups of modern animals—like stony corals, amphibians, birds and mammals—somewhere between 0 and 1 percent of species have gone extinct in recent human history. By comparison, the hellscape of End-Permian mass extinction claimed upwards of 90 percent of all species on earth.

When mass extinctions hit, they don’t just take out big charismatic megafauna, like elephants, or niche ecosystems, like cloud forests. They take out hardy and ubiquitous organisms as well—things like clams and plants and insects. This is incredibly hard to do. But once you go over the edge and flip into mass extinction mode, nothing is safe. Mass extinctions kill almost everything on the planet.

While Erwin’s argument that a mass extinction is not yet under way might seem to get humanity off the hook—an invitation to plunder the earth further, since it can seemingly take the beating (the planet has certainly seen worse)—it’s actually a subtler and possibly far scarier argument.

This is where the ecosystem’s nonlinear responses, or tipping points, come in. Inching up to mass extinction might be a little like inching up to the event horizon of a black hole—once you go over a certain line, a line that perhaps doesn’t even appear all that remarkable, all is lost.

“So,” I said, “it might be that we sort of bump along where everything seems okay and then . . .”

“Yeah, everything’s fine until it’s not,” said Erwin. “And then everything goes to hell.”

Or put another way, mass extinctions may unfold the same way that a dissolute character in Hemingway’s The Sun Also Rises explains that bankruptcies do: “Two ways. Gradually and then suddenly.”

“The only hope we have in the future,” Erwin said, “is if we’re not in a mass extinction event.”

This article has been adapted from Peter Brannen’s new book, The Ends of the World.