Forget the asteroid that killed the dinosaurs. The extinction that almost ended everything happened 185 million years earlier — and it had nothing to do with a rock from space. Ninety-six percent of marine species. Seventy percent of land vertebrates. The largest insect die-off in Earth's history. This is the story of the Great Dying, the worst thing that has ever happened to life on this planet, and why the cause should make you uncomfortable about the world right now.
There is a number that stops people when they hear it for the first time: 96. Ninety-six percent of all marine species gone. Not reduced. Not pushed to the edge. Gone, as in no longer present in the fossil record after a specific horizon in geological time. Add to that 70% of terrestrial vertebrate species. Seventy percent of land animals with backbones, erased in — geologically speaking — almost no time at all. This happened around 251.9 million years ago, at the boundary between the Permian and Triassic periods. Scientists call it the Permian-Triassic mass extinction event, or PTME. Most people who study it call it something older and more honest: the Great Dying. The extinction that killed the non-avian dinosaurs 66 million years ago is the famous one. The one that gets the movies, the museum exhibits, the endless popular science coverage. But the K-Pg event — for all the devastation it caused — was not the worst thing that ever happened to life on Earth. The Great Dying was. It wasn't even close.
The Siberian Traps — a large igneous province covering around 2 million square kilometers — erupted in pulses over hundreds of thousands of years, releasing carbon dioxide, sulfur dioxide, and toxic mercury into the atmosphere and oceans in quantities that destabilized Earth's entire climate system.
What the Permian World Looked Like Before It Collapsed
The late Permian was not a world in obvious decline. It had diversity, structure, established ecological relationships that had been in place for tens of millions of years. In the oceans, the Paleozoic evolutionary fauna — dominated by brachiopods, crinoids, tabulate and rugose corals, bryozoans, fusulinid foraminifera, and trilobites — had been stable since the Ordovician. These weren't struggling holdovers from some earlier age. They were successful, numerous organisms that had survived every extinction that came before them, including several that were themselves significant. On land, synapsids — the group that includes the ancestors of all mammals — were the dominant large vertebrates, particularly the dicynodonts (stocky, beak-mouthed herbivores) and the gorgonopsians (fast predators with large canine teeth). Insects were at their most diverse, with forms flying and crawling through Permian forests that included no equivalent anywhere in the modern world — some with wingspans pushing 70 centimeters. All of that was about to come apart. And the mechanism was not a sudden catastrophe from outside. It built, in pulses, from below.
The Siberian Traps: What It Means When a Continent Erupts
The scientific consensus on the cause of the Great Dying points, overwhelmingly, to flood basalt volcanism — specifically the eruptions that produced the Siberian Traps, a large igneous province that covered around 2 million square kilometers of what is now Siberia with lava. To understand what this actually means, it helps to push past the word "eruption," which carries connotations of localized, dramatic, relatively contained events — Krakatoa, Pinatubo, Vesuvius. The Siberian Traps were none of those things. This was volcanic activity on a continental scale, running in pulses over hundreds of thousands of years, with individual pulses enormous enough to dwarf anything the modern world has experienced in recorded history. The Siberian Traps sat over an unusually dangerous piece of lithosphere. The rocks beneath the eruption zone were rich in halogens — extremely destructive to the ozone layer — as well as thick sequences of carbonate rocks, evaporites, and coal-bearing sediments. When the magma intruded through all of this, it didn't just release the gases produced by melting rock. It cooked the surrounding material. It ignited coal deposits. It baked organic-rich sediments, releasing carbon that had been sequestered for hundreds of millions of years. The result was a cascade of greenhouse gas emissions substantially larger than what the volcanic activity alone would have produced. Atmospheric carbon dioxide, estimated at around 400 parts per million before the extinction, rose to somewhere between 2,500 and 8,000 ppm — depending on the model and the site — during the event. Global average surface temperatures, sitting around 18°C before the crisis, climbed toward 35°C. At high southern latitudes, warming of 10 to 14°C has been recorded in the geological evidence. In what is now Iran, tropical sea surface temperatures that had been between 27 and 33°C jumped above 35°C. On top of the warming, the Siberian Traps released sulfur dioxide in volumes large enough to cause short, sharp volcanic winters — brief but severe cooling events that punctuated the longer warming trend. Mercury poured into the atmosphere and ocean in quantities that left anomalies visible in sediments on every continent. Around 18 teratonnes of hydrochloric acid were emitted. Ozone production dropped by an estimated 60 to 70%, letting ultraviolet radiation reach the surface at levels far above anything organisms had been exposed to in the preceding millions of years.
The Siberian Traps erupted over rock unusually rich in halogens, coal, and organic sediments — meaning the magma didn't just release volcanic gases, it cooked surrounding material and ignited buried carbon stores, multiplying the greenhouse effect far beyond what the eruptions alone would have produced.
What the Oceans Became
Carbon dioxide dissolves in seawater. When you pour enough of it into the atmosphere, you acidify the oceans — and ocean pH dropped by as much as 0.7 units during the Great Dying. For organisms that built shells and skeletons from calcium carbonate, this was chemistry working directly against their ability to exist. But acidification was only one of several things happening to the oceans simultaneously, and it may not have been the primary killer. Warming reduced the solubility of oxygen in seawater. Increased nutrient runoff from soil erosion — itself a consequence of warming and the death of land plants — fed algal blooms that consumed oxygen. Stagnating ocean circulation in a hotter world cut off the delivery of oxygenated water to depth. The oceans, in large parts, went anoxic: starved of oxygen, filled instead with hydrogen sulfide produced by sulfate-reducing bacteria thriving in the dead zones. This condition — called euxinia, oxygen-absent and sulfide-rich — left its signature in the sediment record across the Tethys and Panthalassic Oceans. Biomarkers for green sulfur bacteria, which require both sunlight and hydrogen sulfide, appear in the Permian-Triassic boundary layers at site after site around the world. These bacteria live in the photic zone, the shallow, sunlit surface waters. Their presence means euxinia had pushed all the way up to the surface in shallow seas. The combination — acidification, anoxia, euxinia, heat, mercury poisoning — hit organisms with calcium carbonate skeletons hardest. Corals (tabulate and rugose) lost 96% of genera. Brachiopods lost 96%. Bryozoans lost 79%. Crinoids came within a thread of complete extinction — 98% of genera gone. Foraminifera, 97%. Radiolarians, 99%. Ammonites, 97%, and that was after 30 million years of decline leading into the event. Trilobites, which had been declining since the Devonian and were already reduced to just 5 genera by the late Permian, finally disappeared entirely. They had survived four previous mass extinctions. They did not survive this one. Conodonts — those eel-like vertebrates whose mineralized tooth elements are one of the most useful biostratigraphic tools in geology — were severely affected, though they would survive into the Triassic before going extinct at the Triassic-Jurassic boundary later.
On Land: 70% of Vertebrates, Gone
The terrestrial extinction is harder to pin down than the marine one, partly because the continental fossil record is patchier and partly because the timing on land appears to have varied from region to region — some evidence suggests the terrestrial crisis preceded the marine one, other evidence suggests they were simultaneous or that the land extinction came slightly later in some places. What is clear is that it was severe. Over two thirds of terrestrial labyrinthodont amphibians, reptiles, and therapsid taxa disappeared. All Permian anapsid reptiles except the procolophonids died out. Gorgonopsians — the dominant large predators of the late Permian — went extinct. All dinocephalian genera had already been lost in an earlier extinction event at the end of the Guadalupian, the epoch that preceded the Lopingian. The kill mechanism on land was primarily aridification driven by extreme global warming. The supercontinent Pangaea's interior, already prone to aridity simply by virtue of being far from any ocean, got dramatically drier as temperatures spiked. The Glossopteris flora — the seed fern-dominated vegetation that covered high-latitude Gondwana — collapsed in Australia around 370,000 years before the Permian-Triassic boundary. River systems shifted from meandering to braided patterns, which in fluvial geology is a signature of the widespread death of rooted vegetation that normally stabilizes riverbanks. Insects, which had been more diverse in the Permian than at any point before or since, suffered the largest mass extinction of insects in Earth's history. Eight or nine insect orders became completely extinct. Ten more were heavily reduced. The giant winged forms of the Paleozoic — some of the largest arthropods to ever fly — were gone. The one animal that came through with apparent ease was Lystrosaurus, a pig-sized herbivorous dicynodont therapsid that went on to constitute as much as 90% of some earliest Triassic land vertebrate faunas. The Triassic, in its opening stages, belonged almost entirely to this one genus. The diversity of the Permian world had been replaced by something resembling a monoculture.