Daniel Rothman works on the top floor of the Massachusetts Institute of Technology’s Department of Earth, Atmospheric and Planetary Sciences—a large concrete building overlooking the Charles River in Cambridge. A mathematician by training, Rothman studies complex systems, and he has found a compelling subject in Earth’s behavior. In particular, he investigates the planet’s carbon cycle in the distant past, especially during rare moments when it was pushed past a tipping point and spiraled out of control, taking hundreds of thousands of years to recover.
Since all life on Earth is carbon-based, major disruptions to the carbon cycle are better known as mass extinctions. Geologists have made a troubling discovery in recent decades: many of Earth’s mass extinctions—including the worst one ever—were not caused by asteroid impacts, as once thought, but by massive volcanic eruptions that released catastrophic amounts of CO₂ into the atmosphere and oceans.
If too much CO₂ is released too quickly, it can overwhelm the carbon cycle and trigger a planetary feedback loop. Earth’s natural processes may then amplify the problem, releasing even more carbon and sending the climate into a devastating spiral that lasts for 100,000 years before stability returns. It doesn’t matter whether CO₂ levels are high or low to begin with—what matters is the speed of the change. A rapid increase can lead to disaster.
The carbon cycle normally handles the slow, steady release of CO₂ from volcanoes over millions of years, moving carbon between the air, oceans, and living things before it eventually returns to the Earth. But if a huge amount of carbon is released in a very short time—faster than the planet can absorb—it may set off a chain reaction far more destructive than the initial event. There may be a critical threshold that separates ordinary warming events, which life can adapt to, from runaway extinctions.
Although it’s been more than 60 million years since Earth last crossed such a threshold, Rothman’s research suggests we are now pushing the planet toward that same dangerous path. Once we cross that line, a mass extinction may become inevitable, even if it takes thousands of years to fully unfold.
Throughout Earth’s history, there have been only a few ways to release enormous amounts of carbon from the crust into the atmosphere: rare, massive volcanic events that occur roughly every 50 million years, and—as far as we know—industrial capitalism, which has happened just once.
Mass extinctions are not simply very bad events. They are not civilization-disrupting pandemics like COVID-19, which killed less than 1% of a single primate species. They are not like the loss of a quarter of the world’s vegetation or the glaciation that sterilized much of North America 20,000 years ago. They are not even like supervolcano eruptions, which—though capable of devastating modern society—have had no lasting effect on global biodiversity. These are all part of life’s normal challenges on Earth. Life has endured them before.If it were vulnerable to the kind of routine disruptions that are part of daily life on a volcanic planet. But while Earth is a sturdy world, resilient to all sorts of unimaginable stresses it regularly endures, every 50 to 100 million years something truly catastrophic occurs. These are the major mass extinctions, when conditions on the planet’s surface become so hostile everywhere that they overwhelm the ability of nearly all complex life to adapt.
Five times in the history of animal life, this devastation has reached—and in one case, far surpassed—the somewhat arbitrary threshold of wiping out 75% of Earth’s species, earning the title of “major mass extinction.” Paleontologists refer to these as the Big Five, though the fossil record also shows dozens of other, less severe mass extinctions. The most recent of the Big Five struck 66 million years ago, a global catastrophe severe enough to end the reign of the giant dinosaurs.
It left behind a 110-mile-wide crater, discovered in 1978 beneath Mexico’s Yucatán Peninsula by geophysicists working for the state oil company Pemex. The crater’s size and shape indicated that a six-mile-wide asteroid instantly gouged a 20-mile-deep hole in the ground. Three minutes later, an extremely temporary 10-mile-high mountain range of exploding molten granite surged upward. In the chaos, 76% of animal species were wiped out.
By comparison, the damage humans have inflicted on the rest of the living world is relatively modest so far, accounting for perhaps less than 10% of species lost. At least for now. According to a influential 2011 Nature study by paleobiologist Anthony Barnosky, if we continue at our current rate of extinction, we could escalate from our already alarming level—a minor mass extinction—to the sixth major mass extinction in as little as three centuries or as long as 11,330 years. To future geologists, it would look no different from an asteroid impact. Even more troubling, there may be tipping points along the way where the world’s remaining species vanish almost all at once, like nodes in a power grid failing together during a collapse.
Given how devastating human impact on the biosphere has already been, it’s chilling to consider that the worst of our mass extinction may still lie ahead.
One period in our planet’s history stands out as uniquely instructive—and uniquely chaotic, volatile, and deadly—when it comes to CO2 overload. Three hundred million years ago, Earth repeatedly lost control of its carbon cycle and endured 90 million years of mass extinctions, including two of the worst global catastrophes of all time, both driven by CO2. In one instance, the planet nearly died. Paleontologist Paul Wignall described it as succumbing to “a climate of unparalleled malevolence.” At the very end of the Permian period, 252 million years ago, enough lava erupted from Siberia and seeped into the crust to bury the lower 48 U.S. states under a kilometer of rock.
A kilometer deep.
The remnants of these ancient lava flows are known as the Siberian Traps. Today, they form dramatic river gorges and plateaus of black rock in the remote boreal wilderness of Russia. The eruptions that created them, once covering Siberia in 2 million square miles of steaming basalt, belong to a rare class of giants called Large Igneous Provinces (LIPs).
LIPs are by far the most dangerous phenomena in Earth’s history, with a far more catastrophic track record than asteroids. These once-in-an-era, planet-killing volcanoes are entirely different from typical eruptions like Tambora, Mount Rainier, or Krakatau—or even Yellowstone. Imagine if Hawaii had formed not over tens of millions of years, scattered across the Pacific, but all at once in a brief, violent outburst.In less than a million years, and all in one region—sometimes even bursting through the centers of continents—these massive volcanic events, known as Large Igneous Provinces (LIPs), are Earth’s dramatic reminder that our thin rocky crust and the delicate layer of life covering it rest above a churning, indifferent planetary engine. Here, colossal currents of rock drag entire ocean plates down to the planet’s core to be destroyed and remade. When this process is disrupted, LIPs erupt like tectonic indigestion, flooding vast areas with volcanic rock. If these eruptions are large and rapid enough, they can devastate the world.
At the end of the Permian period, during the greatest mass extinction in history, these eruptions would have produced terrifying explosions, likely causing brief volcanic winters and acid rain. There was widespread mercury poisoning, along with toxic fluorine and chlorine gases—similar to what choked soldiers in World War I trenches. Most critically, and catastrophically for life, the eruptions released a planet-altering amount of carbon dioxide.
Interestingly, as dating of the Siberian lava has become more precise, we now know that the mass extinction didn’t begin until 300,000 years into the eruptions—after two-thirds of the lava had already flooded northern Pangaea with miles-thick rock. This is puzzling. The volcanoes had been spewing their usual deadly mix for hundreds of thousands of years, far surpassing modern industrial pollution. There would have been countless violent explosions and corrosive acid rain storms. Yet life persisted; the biosphere is resilient. So why, after so much sustained devastation, did life suddenly collapse worldwide, even in the deepest oceans on the opposite side of the planet?
What caused the mass extinction? “You can rule the lavas out,” says Seth Burgess, a geologist at the US Geological Survey. But something about these Siberian volcanoes must have changed dramatically after 300,000 years, triggering global collapse. So what was it?
The planet began burning its own fossil fuels.
The result was a massive influx of carbon that overwhelmed Earth’s regulatory systems and pushed the climate out of balance.
Volcanoes naturally emit significant CO₂—up to 40% of the gases from a vent can be carbon dioxide. But after centuries of surface activity, something far more dangerous started brewing underground. Enormous, 1,000-foot-thick sheets of magma, unable to reach the surface, spread sideways through deep rock like glowing roots, heating everything in their path. This is when conditions turned catastrophic.
These subterranean magma intrusions burned through an eight-mile-thick stack of ancient Russian rock in the Tunguska Basin. This geological layer cake included remnants of old salt flats and sandstones, but more critically, carbon-rich limestone, natural gas deposits from ancient seas, and coal from past ages. On contact, the magma ignited these fossil fuels and carbon-rich rocks, triggering massive gas explosions that fractured the overlying rock. At the surface, half-mile-wide craters erupted, releasing gigatons of carbon dioxide and methane into the atmosphere.
After hundreds of thousands of years of typical surface eruptions, the volcanoes had begun burning through the subsurface.The Siberian Traps erupted on a massive scale, acting like enormous coal-fired power plants, natural gas facilities, and cement factories. As one scientist described the end-Permian extinction, “The burning of coal would have represented an uncontrolled and catastrophic release of energy from Earth’s planetary fuel cell.” These eruptions released enormous amounts of CO₂ far too quickly for the planet to absorb.
Here’s a likely sequence of events at the end of the Permian period. First, the excess CO₂ trapped more of the sun’s energy near Earth’s surface—a basic physical process understood by scientists for over 150 years. As a result, the planet warmed by about 10°C over thousands of years, pushing both animal and plant life to their limits. Warmer air also holds more moisture—about 7% more per degree of warming—so as temperatures rose, the water cycle intensified, leading to more frequent and severe storms.
The oceans warmed too, reducing their oxygen content. Marine animals, already struggling in the heat, needed more oxygen, not less. As the seas grew hotter and more stagnant, marine life began to die off. Making matters worse, atmospheric CO₂ dissolved into the ocean as carbonic acid, increasing acidity and depleting the carbonate that many organisms use to build shells. Marine creatures grew weak, sick, or failed to form shells at all.
With ocean life collapsing, the marine food web began to unravel. On land, wildfires destroyed ecosystems and released even more CO₂, while violent storms battered the continents. Debris from the land washed into the sea, carrying nutrients like phosphorus that fueled massive algae blooms. When these blooms died and decomposed, they consumed even more oxygen, suffocating the oceans.
As CO₂ continued to pour from the Siberian Traps, the planet grew hotter, pushing conditions beyond what complex life could endure. In these lifeless, oxygen-deprived seas, ancient anaerobic bacteria—which don’t need oxygen to survive—began to thrive. Some of these bacteria use sulfate for energy, releasing toxic hydrogen sulfide as a byproduct. This gas is deadly to oxygen-breathing life, as seen today in manure pits or around oil fields like those in Texas’s Permian Basin. The poison spread through the deep ocean and into shallower waters.
The world became extremely hot, storm-ravaged, and largely stripped of plant life. The oceans were acidic, oxygen-starved, and emitted poisonous gases from these ancient microbes, killing nearly everything in their path.
Far from the eruptions, in once-forested polar regions like South Africa, rivers that once meandered through rooted landscapes now flowed rapidly over barren ground.Rivers carved braided, sprawling channels across the scoured landscape. Unbearably hot, dry seasons burned the forests, only to be followed by apocalyptic superstorms that washed everything away. The animals that had thrived in those vanished forests for millions of years disappeared too. In the fossil record, fungal spores appear worldwide, marking the collapse of the biosphere. Even insects, whose vast numbers usually protect them from mass extinction, struggled to survive.
While extreme heat devastated life at the poles, Earth’s midsection became truly alien. As CO2 drove global temperatures upward, tropical oceans grew as hot as “very hot soup”—hot enough, perhaps, to fuel monstrous 500 mph “hypercanes” that would have ravaged coastlines. Inland temperatures soared even higher. At its lowest point, much of the planet’s surface resembled the barren landscape of a lifeless exoplanet more than the Earth we know. In fact, the ocean became so empty that reefs worldwide were rebuilt during the recovery not by corals or other extinct marine animals, but by calcified mounds of bacterial slime.
This history is visible even a short hike from my apartment in Boulder, Colorado. Here, in the Front Range—where Earth’s history has been lifted, tilted, and dotted with ponderosa pines—I encounter hummocky red rock formed layer by layer by microbes in a dying sea 252 million years ago. It sits sandwiched between older Carboniferous sandstones and the later Mesozoic sands once trod by dinosaurs, whose remnants now rise behind Denver like a geological backstop. But this thin wedge of bacterial rock, evidence of an ocean briefly ruled by slime, carries terrifying implications.
Soon, nearly every living thing on the planet was dead. The continents fell silent but for scorching winds sweeping over barren wastes—a dry desolation broken only by otherworldly storms that reeked of death. The oceans, once shimmering with schools of vibrant life and colorful reefs, turned putrid, suffocating, and empty, blanketed in slime. Every part of Earth’s interconnected biogeochemical machinery jammed, broke down, or spiraled out of control. Complex life unraveled along with it. All because of too much CO2. If there’s a geological parallel to what industrial civilization has done over the past few centuries, it may be the volcanic activity that triggered the end-Permian mass extinction.
But let’s step back from the brink. However similar our current impact may seem, it’s important to recognize—even emphasize—that the end-Permian catastrophe was unimaginably severe, on a scale humanity is unlikely to ever match. The highest estimates suggest the Siberian Traps volcanoes released up to 120,000 gigatons of CO2—a staggering amount. Even the lower estimates, around 30,000 gigatons, represent volumes so vast that matching them would require burning all the world’s fossil fuels and then continuing to emit carbon for thousands of years—perhaps by industrially burning limestone for generations as the biosphere crumbles. In reality, industrial civilization could theoretically produce about…If the entire world were to unite in a nihilistic, multi-century, international effort to burn all accessible fossil fuels on Earth, it would release about 18,000 gigatons of CO2. However, while the Siberian Traps eruptions produced far more CO2 than our current and future emissions combined, that total was released over tens of thousands of years. What makes our current situation alarming—and why it’s relevant to compare industrial civilization to the Siberian Traps—is that even against those ancient, continent-wide volcanic events, what we’re doing now stands out as unprecedented.
Our highly focused, technologically advanced effort to locate, extract, and burn as much fossil fuel as economically possible, as quickly as possible, has proven remarkably efficient at releasing carbon from the Earth’s crust—even when measured against the largest volcanic events in history. In fact, current estimates suggest we are emitting carbon about ten times faster than the massive, uncontrolled Siberian volcanoes that caused the worst mass extinction ever.
The key issue is the rate of emission. Given enough time, Earth can absorb almost any amount of carbon. Volcanic CO2 is a natural part of the system—without it, the climate wouldn’t be habitable, life would lack essential materials, and oxygen would deplete. But moderation is crucial. To maintain balance, the planet slowly removes CO2 from the atmosphere and oceans, preventing buildup and overheating. This process, however, operates on a geological timescale, storing carbon in coal, oil, gas deposits, and especially ocean sediments that turn into carbonate rock over millions of years.
When large but not extreme eruptions release a surge of CO2, threatening to overwhelm this system, Earth has backup mechanisms. The oceans absorb excess carbon, becoming more acidic, but over millennia, ocean currents carry this acidic water to the seafloor. There, it dissolves carbonate sediments—the accumulated shells of marine organisms over millions of years—acting like an antacid to neutralize the acidity. This is the first line of defense in the carbon cycle, restoring ocean chemistry over thousands of years. Eventually, these processes rebalance the carbon cycle and stabilize the planet. In a world without humans or extreme volcanic events, these feedbacks are usually enough to recover the system. Excess CO2 is turned into rock, temperatures drop, and ocean pH returns to normal over hundreds of thousands of years.
So it’s not just the total amount of CO2 that matters, but how quickly it’s released. A large amount spread over a long time is manageable, but a massive influx in a short period can overwhelm the biosphere.
Unfortunately, the rate at which humans are now releasing CO2 into the atmosphere and oceans far exceeds the planet’s capacity to respond. We are in the early stages of a system breakdown. If we continue much longer, we may witness what true failure looks like.
To push the carbon cycle dangerously out of balance in a short time, you need an intense, rapid infusion of CO2—faster than natural processes like biological activity or weathering can counteract. The modern global industrial effort to extract and burn as much ancient carbon as possible in just a few centuries may be achieving exactly that.
Adapted from The Story of CO2 Is the Story of Everything: A Planetary Experiment.Published by Allen Lane on August 26. To support the Guardian, you can order a copy from the Guardian bookshop. Delivery charges may apply. Listen to our podcasts here and sign up for the Long Read weekly email here.
Frequently Asked Questions
Of course Here is a list of FAQs about the potential for a sixth mass extinction designed to be clear and accessible
BeginnerLevel Questions
1 What is a mass extinction
A mass extinction is a short period of geological time when a high percentage of all living species on Earth die out
2 How many mass extinctions have there been before
There have been five major mass extinctions in Earths history The most famous one 66 million years ago wiped out the dinosaurs
3 What does sixth mass extinction mean
Its the term scientists use to describe the current rapid loss of species across the planet which is happening at a rate much faster than what is considered natural
4 Whats causing this potential sixth extinction
Unlike past extinctions caused by asteroids or volcanoes this one is primarily driven by human activities The main causes are habitat destruction climate change pollution overhuntingfishing and the spread of invasive species
5 Is this really happening or is it just a theory
The dramatic increase in extinction rates is a welldocumented scientific observation not just a theory The debate among experts is not if its happening but how severe it will become and what we can do to mitigate it
6 Are humans going to go extinct too
It is highly unlikely that Homo sapiens would go completely extinct from this event However the collapse of ecosystems that provide us with food clean water and stable climates could cause widespread societal collapse and human suffering
Intermediate Advanced Questions
7 How do scientists know the extinction rate is higher than normal
They compare the current rate of species loss to the background extinction ratethe average rate of extinction that occurred naturally over millions of years before modern human influence The current rate is estimated to be tens to hundreds of times higher
8 What are some examples of species that have recently gone extinct
Wellknown examples include the Tasmanian tiger the passenger pigeon the Pyrenean ibex and more recently species like the Bramble Cay melomys and the Chinese paddlefish Many lesscharismatic insects amphibians and plants are lost every year without much notice
