Some 250 million years ago, the organisms of Earth were having a very bad time—the very worst time, you might say. The Permian-Triassic extinction event was unfolding, in which 70 percent of land species and 96 percent of marine species disappeared. Runaway global warming had raised equatorial ocean temperatures to 104 degrees Fahrenheit. The seas rapidly acidified, so shelled critters struggled to build their protective homes. Indeed, the fossil record shows these species got it the worst—strong evidence that the extinction’s culprit was CO2 mucking with the oceans’ pH balance, and the rest of the planet, for that matter. Every decade or so, ozone-eating gases would dissolve Earth’s protective layer in the sky, irradiating plants and animals, before the ozone layer closed up. This happened again and again, allowing periodic blasts of extreme radiation to bombard the planet.
One long-standing hypothesis for the cause of the Permian-Triassic extinction, also known as the Great Dying, will sound worryingly familiar to us modern humans: the large-scale burning of coal. Only such a catastrophe, scientists reckoned, had the power to transform Earth so radically in such a short period of time; the fossil record indicates that species weren’t dying off en masse over millions of years, or hundreds of thousands of years, but tens of thousands of years. A carbon-spewing volcanic event alone—even the biggest of booms—couldn’t explain such a cataclysm. And there’s no evidence of an asteroid strike in this period, like the one that would kill off the dinosaurs 190 million years later.
It’s a juicy theory. The only problem is that scientists didn’t have the hard evidence to prove a massive combustion of coal did all those species in. But they knew where to look: in what we now call Siberia, a frigid expanse of land that 250 million years ago was anything but chilly, because it was flooded with lava. Volcanoes pumped out so much planetary goop that the stuff could have covered the entire continental United States a half-mile deep. And unfortunately for all life on Earth, scientists suspected, the lava was flash-incinerating vast deposits of coal and ejecting massive quantities of greenhouse gases into the atmosphere.
That’s how the theory goes, anyway.
Planetary scientist Lindy Elkins-Tanton, of Arizona State University, was on a mission to prove it. But she was stymied by the fact that the evidence she coveted lay in areas the Russian government doesn’t let its own citizens visit, much less foreign researchers. But Elkins-Tanton eats bureaucrats for breakfast. After cutting through spools of red tape for half a year, in the summer of 2008 she and her team flew from Moscow to the tiny Arctic town of Khatanga, north of the expanses the team needed to penetrate. Home to a thousand people, it’s a launching pad for Arctic scientific expeditions—a good place to stop if you’re headed to the Taymyr Peninsula to the north, for instance, to look for frozen mammoths.
To get there, though, the scientists had to hop on a … let’s say unorthodox flight, from a small airport in Moscow. When they boarded, they found that their seats had been piled high with baggage and boxes—the other passengers were returning to Khatanga for the summer. “Some people started piling luggage off of three seats, so we could sit down,” says Elkins-Tanton. “And the plane was so heavily loaded that it almost hit the trees during takeoff. It went way past the end of the runway and almost didn't make it.” Spooked, but nevertheless having reached cruising altitude, she and two colleagues decided to get up and find their friends seated elsewhere on the plane. “We unbuckled our seat belts and stood up, and the seats fell over backward, because they weren’t bolted to the airplane,” she says.
Scientists. So picky.
From Khatanga they flew in an old Soviet troop-transporting helicopter—still pocked with bullet holes—to the Kotuy River, a cold, muscular Arctic rager that ideally they’d tackle in one of those fancy Zodiac motor boats. “We'd been begging our Russian friends, ‘Just let us buy some Zodiacs. We'll ship them up there. It'll be the best way to go,’” says Elkins-Tanton. “They're like, ‘No, no, no—no one else would like it. If we had Zodiacs and they didn't have Zodiacs, it would look really bad. It would ruin all the collaborations. We can’t have Zodiacs.’”
“And they're like, ‘Don't bring life preservers. That's really insulting.’”
Floating down the river in less fancy boats, dutifully bereft of life preservers, they pulled into any promising outcrop that might offer geological clues about the explosive incineration of coal—volcanic rocks were a good indicator. If they found a particularly choice spot, they’d stop and set up camp for a few days, surveying the permafrost landscape and summiting cliffs. This far north, the sun was out 24 hours a day in summer, and during the peak of the day, that permafrost tended to thaw out.
“We'd be in our tents and we would just hear these gigantic roaring landslides as the permafrost gave way, and whole sides of these cliffs slipped down as mud and huge amounts of trees,” Elkins-Tanton says. “Sometimes we'd be climbing up those cliffs during the day, and we’d get to these places that were really hair-raising. I didn't quite get it—I didn't put it together in my head—until one of my colleagues said, ‘You know, the reason we're sinking almost to our knees in mud here is because all this permafrost is melted, and probably tomorrow it'll landslide.’”
Elkins-Tanton and her colleagues scoured the Siberian landscape, chisels and small 10-pound sledgehammers in hand. They were looking for hard evidence of a cataclysm that might have kicked off the Permian-Triassic extinction: volcaniclastic rock—crumbly stuff, with lots of small particles stuck together, almost like sandstone.
“I really wanted to find this place that was rumored where there were a lot of rocks that result from explosive volcanic eruptions,” Elkins-Tanton says, “because that's the only way that we know of that you can effectively drive chemicals into the upper atmosphere where they'll get spun around the whole planet.” She was closing in on the geological signals of apocalyptic climate change.
Before this region of Siberia tried to destroy all multicellular life on the planet, it was a peaceful inland sea, which dried up and left an “evaporite basin.” The water’s evaporation deposited a layer of limestone and minerals rich in chlorine and bromine—think of it as being like the gunk that’s left when you forget coffee or tea in a cup. Eventually, a swamp grew on top of this mineral layer. As plants and animals decomposed, they deposited layers of coal, oil, and gas. “So basically that whole area of central Siberia is just like a layer cake of toxic material, all created by Mother Nature,” says Elkins-Tanton.
The secret ingredient of this layer cake is magma, which flowed from deep below and injected itself between layers of toxic sedimentary rock, formed from the dried-out sea. “Coal was the last thing on the top, but we know coal covered the whole basin,” Elkins-Tanton says.
To cause a mass extinction that unfolded over a mere tens of thousands of years, somehow all that carbon had to suddenly burn off and rapidly warm the whole planet. “There's only a few things that cause global change like that,” Elkins-Tanton says. “One is a giant meteor strike, which—there's no evidence for it. It would have to be a really big one, and the evidence would be there. Another one is a nuclear war—pretty sure that did not happen.”
A third option, Elkins-Tanton continues, is “you've got to figure out a way to change the whole atmosphere. And the way to change the whole atmosphere is to drive chemicals up into the stratosphere.” For that, you need an explosive volcanic eruption and, critically for Elkins-Tanton, you need the rocks to prove it.
Not all volcanoes are so ornery. For example, Kilauea isn’t explosive at the moment, because its magma (what you call the gooey stuff while it’s still underground—it becomes lava when it emerges) is relatively thin and runny. When Kilauea’s magma bubbles to the surface, it releases its gases in an orderly fashion.
Mount St. Helens, on the other hand, teemed with relatively thick magma, which better traps gases. As it ascends, the mass of magma suddenly becomes more buoyant, and it expands. And that means a bigger blowout. “If you have enough gases in the magma, instead of it bubbling out like soup, it explodes like a shaken soda bottle,” Elkins-Tanton says. “The carbon dioxide in soda is in solution. It's not in the form of bubbles until you shake it up or open it. And that's the same as releasing pressure as the magma comes closer to the surface, and all the volatiles form bubbles.”
“That's like Pinatubo or Mount St. Helens, but on a much bigger scale,” she continues. “And those things have enough heat and gases that they rise all the way up and puncture through the tropopause into the stratosphere.” The tropopause is a boundary layer between the troposphere—the bit of atmosphere that we call home—and the stratosphere, which starts about 6 miles up. The troposphere is relatively chaotic, filled with all kinds of clouds, winds, and weather systems, whereas the stratosphere is relatively calm. (Planes fly in this zone to avoid turbulence, in fact.)
This calmness, though, helped doom all those species 250 million years ago: Explosive volcanic eruptions in Siberia punched through the tropopause and deposited great burps of carbon into the stratosphere. If all that gas had stayed in the troposphere over Siberia, it would have stayed more local and gradually dissipated. Life would be miserable for plants and animals below, to be sure, but the rest of the Earth would have been spared a mass extinction. Instead, it spread around the world as an insulating layer of greenhouse gas.
But the eruptions themselves were only one component of the catastrophe; they alone couldn’t have led to such intense and rapid global warming. Elkins-Tanton and her colleagues were looking for evidence that the large-scale burning of coal also helped do in life on Earth. Floating down the rivers of Siberia during six separate expeditions—in inflatable boats that refused to stay inflated—Elkins-Tanton searched for evidence in the cliff faces, the places where it had all popped off a quarter billion years ago. “Every single cliff along the river was these explosive volcanic rocks, from the water level up to the top,” says Elkins-Tanton. “Sometimes 100 meters or more of cliff, just explosive rocks.”
Drudging through thawing permafrost, collecting hundreds of pounds of rocks and squirreling them away in heavy-duty plastic bags, Elkins-Tanton stumbled upon a peculiar kind of rock—they contained little bits of both coal and charcoal. “We weren't totally clear what they were, and some of the people in the field with me were not very interested. But I don't know, they seemed really unusual to me, and so I was taking care to sample them,” says Elkins-Tanton.
Then she remembered the work of Stephen Grasby, senior research scientist at the Geological Survey of Canada. On the other side of the North Pole, in the Canadian Arctic islands, he and his colleagues had previously discovered bizarre formations called cenospheres in rocks dating back 250 million years. “They are coal experts, and they knew that the only way these little, hard, burnt bubbles of carbon are made in the current day is in super-high-temperature, coal-burning, power stations. They were not aware of them having ever been found in the geologic record before,” Elkins-Tanton says. “And they hypothesized that they were from coal burning in Siberia from the Siberian flood basalts, and that they'd been carried around the globe on these Arctic air currents and fallen in the north of Canada.”
And so it all came together. Elkins-Tanton had found the rocks indicative of violent explosive eruptions that she and her team think had flash-incinerated vast deposits of coal, “degassing” the fossil fuel and propelling CO2 into the stratosphere. This allowed particulate matter and greenhouse gases, suspended in the relatively calm stratosphere, to spread around the world.
“Then, of course, all the animals and plants died,” Elkins-Tanton says. “So this is the first actual evidence—field evidence, physical evidence—for coal burning at the flood basalts in Siberia.” (She and Grasby and their colleagues recently reported their findings in the journal Geology.)
Geologists actually suspected that they had already found this carbon in the fossil record. The ocean absorbs CO2 from the atmosphere, and in turn sea creatures incorporate carbonate into their skeletons and shells, before dying and sinking and becoming limestone. Because the average isotopic weight of carbon atoms derived from organic sources is lighter than those derived from the mantle of the Earth, scientists can analyze limestone and show a sudden surge in light carbon, indicating a surge in atmospheric CO2. But this new study is the first to put hard evidence to the mechanism for how that carbon got there, how explosive volcanoes lit fields of Siberian coal afire and flooded the stratosphere with greenhouse gases.
“That provides us now with a smoking gun—or smoking coal, I guess—evidence that there really was degassing of these coals during the eruptions,” says Stanford University paleontologist Jonathan Payne, who wasn’t involved in the study. “This is really heroic field work.”
But how much degassing, exactly? Elkins-Tanton and her colleagues have calculated that the Siberian eruptions that burned coal and other organic matter could have pumped 6,000 billion to 10,000 billion tons of carbon into the atmosphere. “The exact quantity is still hard to pin down directly by geological observations,” says Payne. “A lot of this then is a question of scaling up and making the assumption that what we see in the field is representative, and that's a perfectly reasonable assumption.” Payne adds that he wouldn’t be surprised if the high-end figure of 10,000 billion tons of carbon is in fact low, once you factor in the potential obliteration of rock like limestone, which sequesters its own carbon.
Now for a bit of scary perspective. According to the Global Carbon Project, a consortium of climate researchers, we humans emit nearly 40 billion tons of CO2 a year, and that’s been increasing reliably by a few percent each year, throwing Earth’s carbon cycle out of whack. Typically, the CO2 system works like filling up a bathtub with an open drain. Volcanoes and tree-burning wildfires release the gas, some of which enters the atmosphere and decays over time, some of which gets absorbed by the ocean. But we as a species are now pumping way too much extra CO2 into the atmosphere. The faucet is turned up too high, and the drain can’t keep up, so the tub is overflowing. The consequence is rapid global warming.
In the same way, volcanic chaos in Siberia 250 million years ago cranked up the CO2 faucet, and the bathtub overflowed. “The Earth doesn't care what is doing the work,” says research geologist Seth Burgess of the US Geological Survey. (Burgess didn’t coauthor the Geology paper, but did accompany the team on field expeditions.) “At the end of the Permian, we have evidence for this huge slug of greenhouse gases going into the atmosphere. The biosphere responded with 90 percent mortality at a species level. The Earth doesn't care what's doing the driving—it's going to respond the same way. So we can learn about what's very likely to happen if we put levels of greenhouse gas into the atmosphere at the same pace as occurred at the end of the Permian.”
It’s still unknown how the rate of emissions at the end of the Permian compares to how fast we’re burning fossil fuels today—the researchers can calculate how much carbon Siberia injected into the atmosphere, but not how quickly. Still, Burgess continues, with our current carbon emissions, “we could make life for our species pretty difficult. The Earth is going to be fine, and lots of species will be fine. Many things will survive if our species decides to shoot itself in the foot. But the analogy is there. We know what happens when you significantly increase the amount of greenhouse gas in the atmosphere on a short, short timescale.”
And our species isn’t just sullying the planet with greenhouse gases. There’s deforestation, microplastic pollution, and any number of other environmental sins, all compounding one another to form a super-crisis. “The Permian doesn't have any analogue to human changes in land use, overhunting, overfishing,” says Payne. “Some of the things humans are doing are really different from anything that would have happened in the Permian. But some of the big changes we’re causing to the planet are the same ones that appear to have been instrumental in the End-Permian extinction.”
To humanity’s credit, and more specifically Elkins-Tanton’s, science has been able to look back a quarter billion years and piece together a remarkably detailed story about a very bad time on Earth in the only way that’s available to us, which is through the geologic record. “There's no do-over,” says Elkins-Tanton. “You can't do a double-blind experiment. You can't even do one experiment.”
But scientists can gather observations that allow them to time-travel to an unrecognizable Siberia, and an unrecognizable Earth. They know the planet got real hot real quick, consistent with a burp of carbon dioxide. They see that carbon in the fossil record. They’ve got rocks that suggest explosive eruptions fundamentally changed the atmosphere. And they know that multicellular life almost ceased to exist.
Carbon dioxide doesn’t get all the blame here—scientists know that the eruptions released so much sulfur that the resulting acid rain turned some parts of the sea to lemon juice. “We know that other things also happened to add to the global catastrophe,” says Elkins-Tanton. “But this was a really key missing link that now has been found.”
Getting that missing geological link into a lab for analysis meant lugging almost 400 pounds of rocks out of Siberia. To conclude their expedition, the team helicoptered back to Khatanga, then booked passage in a cargo plane, because a commercial flight would have been too expensive. “Even the one with the unbolted seats, because we'd have to pay this huge amount of money per kilogram, and we have like 180 kilograms of rocks,” Elkins-Tanton says.
Standing on the tarmac, they watched a forklift load their container of priceless scientific material into the belly of the machine. But their own onboarding would not be so easy. “The way you get in the plane is you climb up a wooden ladder holding onto a rope with knots in it,” says Elkins-Tanton. “We get in there, and of course there's people in the plane already. The only seats are little jump seats that pull down from the walls of the plane, and they're all taken.” So the scientists sat on the cold steel floor of the plane, save for takeoff and landing, when they had to stand up and wrap their arms around poles.
“There's a navigator sitting at a desk with a protractor, plotting our flight path,” she adds. “Then part way through this flight, which is three or four hours, we notice this bad smell. We get up to walk around the plane—because it's not like there are flight attendants or anything. We walk to the back of the container that has our rocks in it, and it turns out the whole back of the plane is packed with frozen, skinned caribou. And they're beginning to thaw.”
Ain’t the continuing existence of life on Earth grand?