When Life Nearly Vanished

When massive Siberian volcanoes reshaped Earth’s climate and oceans, life nearly vanished in the greatest known mass extinction about 252 million years ago.

What would it take to almost empty the oceans? Not just damage a reef, not just wipe out one famous group of animals, but remove most marine species from Earth. About two hundred fifty-two million years ago, at the end of the Permian Period, that is what happened in the largest mass extinction known from the fossil record.

In the last episode, we stood in the Carboniferous coal forests, among giant club mosses, huge arthropods, and air richer in oxygen than today. But Earth did not remain a greenhouse of endless swamps. Over tens of millions of years, the continents kept moving until, by the late Permian, they had joined into Pangaea, a supercontinent stretching almost from pole to pole.

That arrangement mattered. A coastline softens climate, the way a nearby ocean can keep western Europe milder than places at the same latitude deep inside a continent. Pangaea had an enormous interior far from the sea, so many regions were dry, seasonal, and harsh. Life still flourished, but it was different from the coal-swamp world: reptiles, amphibians, and mammal relatives on land; brachiopods, corals, sponges, ammonoids, and many other animals in the seas.

Then came the catastrophe often called the Permian-Triassic extinction, or the Great Dying. Scientists estimate that a very large majority of marine species disappeared, often described as around ninety percent, though the exact number depends on how fossils are counted. Land vertebrates, insects, and plants were hit hard too. This was not the asteroid story from the end of the dinosaurs. The main suspect here was fire from inside Earth.

At roughly the same time, enormous eruptions began in what is now Siberia. These eruptions formed the Siberian Traps, vast layers of flood basalt. Imagine not one neat cone like Mount Etna or Mount St. Helens, but repeated lava floods spreading across huge areas, over many thousands of years or more. The lava devastated nearby regions, but the gases changed the whole planet.

Volcanoes released large amounts of carbon dioxide and other gases into the atmosphere. Carbon dioxide traps heat, and when enough is added quickly by geological standards, the climate warms. Think of turning up the thermostat in a room that contains not furniture, but oceans, winds, rainfall, soils, reefs, and every food web on Earth.

Warming was dangerous by itself, but the oceans made it worse. Warm water holds less oxygen than cold water, rather like a warm soda losing its fizz faster than one pulled from the fridge. Warmer seas can also become more layered, with less mixing between the surface and the depths. If oxygen is not carried downward, deep water can become oxygen-poor, or anoxic.

For many marine animals, that meant slow suffocation. Creatures living on the seafloor could not simply migrate to a cleaner, cooler room. Reefs collapsed, burrowing animals vanished, and food chains broke. Some evidence also points to euxinia, when water is not only low in oxygen but rich in hydrogen sulfide, a poisonous gas produced by certain microbes in oxygen-starved settings.

Carbon dioxide also changes seawater chemistry. When it dissolves into the ocean, it can drive acidification, making it harder for animals to build shells and skeletons from carbonate minerals. That would have been especially damaging to reef builders and shelled organisms. So the crisis was not one weapon. It was an arsenal: heat, low oxygen, chemical stress, and habitat collapse.

There were probably extra complications. As magma pushed through coal beds, salt deposits, and organic-rich rocks, it may have baked them and released additional greenhouse gases and toxic compounds. Researchers have also discussed possible ozone-layer damage, methane release, and metal pollution. These details are still studied and debated, but the broad picture is firm: massive volcanism disrupted the atmosphere and oceans on a planetary scale.

Was there truly a single day when life almost disappeared? No. That phrase captures the drama, not the timetable. In human terms, the extinction may have unfolded over a long span. In geological terms, it was shockingly fast, leaving a sharp break between rich late Permian ecosystems and the poorer world that followed.

Recovery was slow. For millions of years after the extinction, ecosystems remained simplified. Some survivors became famous because they were so common afterward. On land, Lystrosaurus, a sturdy beaked synapsid about the size of a pig or a medium dog depending on the species, spread widely across parts of Pangaea. In the seas, hardy organisms moved into the emptied space.

But recovery did not mean rewinding Earth. The Permian world was gone. The Triassic world that followed would eventually bring new reef systems, marine reptiles, early dinosaurs, and the first true mammals. Mass extinction is not only an ending; it is a brutal reset of evolution’s stage.

So the Great Dying teaches a stark lesson. Life is resilient, but not invulnerable. When the atmosphere changes, oceans warm, oxygen runs low, and chemistry shifts, even ancient, well-established ecosystems can unravel. Two hundred fifty-two million years ago, life did not vanish completely, but it came closer than at any other known moment in its long history.