What Was the Permian Extinction? The Day Life Nearly Ended
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Around 252 million years ago, roughly four out of every five species in the oceans and most of the large animals on land disappeared within a geological instant. The event that ended the Permian period is the closest life on Earth has come to being wiped out, far worse than the asteroid strike that later killed the dinosaurs, and the evidence points to a cause that is uncomfortably familiar: an enormous, fast release of carbon into the atmosphere.
The scale of the loss
Palaeontologists estimate that about 81 percent of marine species and around 70 percent of land vertebrate species died out, along with most insects, the only mass extinction known to have hit insects hard. The trilobites, which had lived in the seas for 270 million years, vanished completely. Reef systems collapsed and did not rebuild for millions of years, and there is a stretch of rock in many parts of the world containing almost no fossils at all, a coal gap where no coal formed because there were too few plants to make it.
The victims were not obscure. The Permian world had been full of large, strange animals: sail-backed synapsids such as Dimetrodon, and the therapsids that were on the way to becoming mammals. Most of those lineages ended. What came through was a thin sample of what had existed before.
A million years of eruptions
The prime suspect lies in Siberia. The Siberian Traps are the remains of one of the largest volcanic events in Earth's history: not a mountain erupting but a region the size of western Europe pouring out lava through fissures for something like a million years, leaving basalt in places several kilometres thick. Precise dating of the lava and of the extinction layer in rocks elsewhere shows the two coincide.
Lava alone would not have done it. The magma rose through thick beds of coal, oil and limestone, cooking them and releasing carbon dioxide and methane on a scale no ordinary eruption produces, along with sulphur and halogens that thinned the ozone layer. Estimates of the carbon released run into the tens of thousands of billions of tonnes, arriving over a few thousand years at a time.
How the killing happened
The carbon warmed the planet by something like 10 degrees Celsius, and the warming did most of the damage indirectly. Warm water holds less oxygen, so the oceans began to suffocate. Dissolved carbon dioxide made seawater more acidic, which dissolved the shells of the animals that built them. As the deep ocean lost oxygen, bacteria that breathe sulphate instead thrived and pumped out hydrogen sulphide, which is poisonous to almost everything and may have leaked into the air. Sea surface temperatures near the equator may have reached 40 degrees, hotter than most animals can survive.
The evidence for each step is written in the chemistry of the rocks: a sharp shift in carbon isotopes marking the release, a spike in mercury from the volcanism, the disappearance of oxygen-loving species before oxygen-tolerant ones, and shells that grew thinner before they stopped appearing altogether.
A slow recovery, and a new cast
Life did not bounce back. The early Triassic that followed stayed hot and unstable for several million years, and it took perhaps ten million years for ecosystems to regain their former complexity, the longest recovery after any extinction. For a while a single pig-sized plant-eating animal, Lystrosaurus, made up the great majority of land vertebrate fossils across the entire planet, a sign of how empty the world had become.
The emptiness also created the opening for what came next. With the synapsids reduced to a remnant, a different group of reptiles, the archosaurs, spread into the vacant space, and within the Triassic they had produced crocodiles, pterosaurs and the first dinosaurs. The age of dinosaurs began in the aftermath of the Great Dying, and the surviving synapsids, small and mostly nocturnal, were the ancestors of mammals.
Why it is studied so hard now
The Permian extinction is the best natural experiment on record for what a large, rapid injection of carbon does to a planet, which is why climate scientists read the literature as closely as palaeontologists do. The Siberian Traps released carbon over thousands of years; human activity is currently releasing it at a rate estimated to be at least ten times faster, although the total so far is a small fraction of what the eruptions eventually delivered. The sequence of consequences, warming, ocean deoxygenation and acidification, is the same one being measured today at a much smaller scale. The chain of events, in order:
- •Flood basalt eruptions burn through coal and carbonate rock
- •Carbon dioxide and methane warm the planet by around 10 degrees
- •Oceans lose oxygen and turn acidic, reefs and shelled animals die
- •Hydrogen sulphide and ozone loss poison land and sea
- •Around 80 percent of species gone, recovery takes millions of years
The takeaway
The end-Permian extinction, 252 million years ago, killed most species on Earth after a million years of Siberian eruptions burned through carbon-rich rock and cooked the planet. It cleared the way for dinosaurs and mammals, and it remains the clearest warning in the geological record of what a fast carbon release can do.