The Great Dying, formally known as the end-Permian mass extinction, was the worst biological catastrophe in Earth’s history. Roughly 252 million years ago, an estimated 80 to 96 percent of all marine species and a comparable share of land-dwelling species vanished in a geologically brief window, possibly as short as 60,000 years. The trigger was a massive volcanic episode in what is now Siberia, but the killing was done by a cascade of interlinked environmental crises: extreme warming, ocean acidification, oxygen-starved seas, ozone destruction, and wildfire. Understanding how all these mechanisms fed on each other is what makes the Great Dying such a compelling and unsettling chapter of Earth’s past.
How Fast Did It Happen
Geologists have spent decades refining the timeline. High-precision uranium-lead dating of volcanic ash beds at the global reference section in Meishan, China, places the main extinction pulse between about 251.94 and 251.88 million years ago, an interval of roughly 60,000 years with an uncertainty of about 48,000 years either way.1PubMed Central. High-precision timeline for Earth’s most severe extinction That is a blink in geological time. Some researchers have argued for an even tighter pulse, but even the broader estimates put the worst of the crisis inside a window shorter than many ice ages.
The extinction did not hit all at once like a light switch. Geochemical records from deep-water sections in South China show at least two distinct episodes of mercury enrichment, a chemical fingerprint of volcanic activity. The older episode came before the main carbon-isotope crash that marks the extinction, while the second fell between about 251.8 and 251.6 million years ago, coinciding with the deepest point of carbon-cycle disruption.2Geochemistry, Geophysics, Geosystems. Timing and Provenance of Volcanic Fluxes Around the Permian‐Triassic Boundary Mass Extinction in South China So the catastrophe had precursors and aftershocks. Life was being stressed well before the final hammer blow, and conditions stayed hostile long after.
The Siberian Traps and the Carbon Bomb
The ultimate cause was volcanism on a scale difficult to imagine. The Siberian Traps, a large igneous province, erupted enough lava to cover millions of square kilometers. But it was not the lava itself that did the most damage. On its way to the surface, magma intruded into sedimentary basins rich in organic carbon, limestone, and evaporites. Contact metamorphism, basically the baking of buried sediments by hot magma, released staggering volumes of carbon dioxide and other gases. Thermal modeling of drill cores from the Tunguska Basin shows that sill intrusions could generate 52 to 80 tonnes of CO₂ per square meter, and only about one percent of the sill-affected area would be needed to release a thousand billion tonnes of CO₂.3PubMed Central. Sills and gas generation in the Siberian Traps The total affected area was vastly larger than that one percent.
Quantitative modeling of ocean pH proxies and carbon-isotope records points to a total carbon release of around 36,000 billion tonnes, injected at a rate of roughly 5 billion tonnes of carbon per year. The source was overwhelmingly volcanic in character.4PubMed Central. Massive and rapid predominantly volcanic CO(2) emission during the end-Permian mass extinction For perspective, modern human emissions are roughly 10 billion tonnes of carbon per year, meaning the end-Permian injection rate was in the same order of magnitude as today’s. The difference is that it sustained that pace for tens of thousands of years, building up to concentrations the planet had not experienced in hundreds of millions of years.
Mercury spikes in terrestrial rock sections separated by thousands of kilometers, from equatorial South China to high-latitude central Asia, confirm the global reach of the Siberian Traps’ emissions. Unusual mercury-isotope signatures at these sites are consistent with massive volcanogenic inputs, and they line up precisely with the negative carbon-isotope excursion that marks the extinction.5Geology. Mercury evidence of intense volcanic effects on land during the Permian-Triassic transition
A World That Overheated
All that carbon dioxide did what carbon dioxide does: it trapped heat. Before the extinction, tropical sea-surface temperatures sat around 22 to 25 °C and atmospheric CO₂ hovered somewhere between 500 and 4,000 parts per million. During the peak of the crisis, tropical ocean temperatures climbed to around 30 °C and CO₂ may have reached 8,000 ppm.6Earth-Science Reviews. Global warming and the end-Permian extinction event: Proxy and modeling perspectives The warming was not sudden in absolute terms. Oxygen-isotope data from brachiopod fossils suggest that seawater temperatures began climbing at least 300,000 years before the main die-off, with a gradual rise of about 12 °C that progressively degraded ecosystems until the final collapse.7Palaeontology. Gradual warming prior to the end‐Permian mass extinction
The heat did not relent after the extinction either. Early Triassic temperatures remained lethally high in equatorial regions for millions of years. Fossil evidence shows the near-complete absence of fish and calcareous algae near the equator, along with a dominance of tiny invertebrates, during thermal peaks. Most plants and land animals were effectively driven out of the tropics.8PubMed. Lethally hot temperatures during the Early Triassic greenhouse Temperatures of 35 to 40 °C on land would have been fatal for most organisms that did not migrate poleward.9PubMed Central. Hyperthermal-driven mass extinctions: killing models during the Permian–Triassic mass extinction
Poisoned Oceans
The oceans suffered through several overlapping crises at once. Acidification was one of the deadliest. The rapid injection of volcanic CO₂ drove a sharp drop in ocean pH, and the second extinction pulse in particular is linked to an abrupt acidification event that preferentially wiped out marine animals with heavily calcified shells and skeletons.10PubMed. Ocean acidification and the Permo-Triassic mass extinction Independent evidence from sulfur isotopes in mineral crystals formed in acidic conditions confirms that seawater acidified suddenly during the extinction interval, broadly supporting what boron-isotope studies had already shown.11Global and Planetary Change. A rapid onset of ocean acidification associated with the end-Permian mass extinction Not all researchers agree on how severe or prolonged the acidification was; one recent review describes the proxy evidence as “conflicting.”12PubMed Central. The great catastrophe: causes of the Permo-Triassic marine mass extinction But the general picture, that at least one severe acidification pulse occurred, is well supported.
Oxygen loss was arguably even more devastating. Warming oceans hold less dissolved oxygen, and the sluggish circulation of the late Permian ocean, driven in part by the configuration of the supercontinent Pangaea, made things worse. The result was a dramatic expansion of anoxic (oxygen-free) and euxinic (hydrogen-sulfide-rich) zones. Biomarker and iron-chemistry analyses from sites in Australia and South China show that toxic, sulfide-laden waters invaded the sunlit upper ocean, a condition called photic-zone euxinia. Hydrogen sulfide is lethal to most marine animals at low concentrations, and its widespread presence likely contributed both to the killing itself and to the agonizingly slow pace of recovery afterward.13PubMed. Photic zone euxinia during the Permian-triassic superanoxic event The expansion of these dead zones was not just a side effect of poor circulation. It was actively amplified by warming-driven increases in biological productivity and carbon recycling, creating a feedback loop that kept the oceans hostile.14PubMed Central. Flourishing ocean drives the end-Permian marine mass extinction
What Happened on Land
Terrestrial ecosystems may have started collapsing before the marine crisis peaked. Organic geochemical records from multiple sites show evidence of widespread soil erosion and ecosystem breakdown near but slightly before the main marine extinction horizon.15Global and Planetary Change. Terrestrial ecosystem collapse and soil erosion before the end-Permian marine extinction Forests were dismantled in stages. During the main crisis phase, coal seams disappeared entirely, charcoal concentrations spiked (indicating intense wildfires), and soil erosion accelerated dramatically. A later phase saw even more volcanism and erosion but fewer fires, suggesting the climate had shifted back to wetter conditions that made burning less likely, though the forests were already gone.16Earth and Planetary Science Letters. Stepwise deforestation during the Permian-Triassic boundary crisis linked to rising temperatures
One of the more striking consequences was the destruction of the ozone layer. Volcanic emissions, especially organohalogens released during the metamorphism of salt-bearing sediments, appear to have thinned or punctured the stratospheric ozone shield. Fossil pollen and spores from the latest Permian show a sharp increase in UV-absorbing compounds, a direct biological response to elevated ultraviolet-B radiation. This UV spike coincides with mercury peaks and the carbon-isotope crash, tying it to the same volcanic source.17PubMed Central. Dying in the Sun: Direct evidence for elevated UV-B radiation at the end-Permian mass extinction Elevated UV can cause genetic mutations in plants, and abnormal spores found in end-Permian sediments globally have been interpreted as evidence for widespread mutation driven by UV stress.18PubMed Central. Environmental mutagenesis during the end-Permian ecological crisis
The climate of Pangaea was already harsh before the crisis. With most of Earth’s landmass fused into one supercontinent, conditions were extremely continental: winter temperatures in the southern polar regions dropped to around −25 °C while subtropical summers exceeded 45 °C, and aridity dominated everything except the coasts and high latitudes.19Journal of Geophysical Research: Atmospheres. Pangaean climates: Megamonsoons of the megacontinent Layer extreme greenhouse warming on top of that, and you get a world where the interior of Pangaea became uninhabitable for most complex life.
Why Some Animals Survived and Others Didn’t
The extinction was not random. In the oceans, physiology mattered enormously. A 2024 study found that marine animals carrying oxygen-transport proteins with higher carrying capacity, like hemoglobin and hemocyanin, survived far better than those relying on less efficient proteins like hemerythrin, or those that simply absorbed oxygen through diffusion. Groups with better oxygen delivery could cope with low-oxygen waters and meet the increased energy demands imposed by acidification.20PubMed Central. Respiratory protein-driven selectivity during the Permian-Triassic mass extinction This explains a pattern that had puzzled paleontologists for years: why some heavily calcified groups were devastated while others, seemingly just as vulnerable, scraped through. The answer was partly about breathing, not just about shells.
On land, the pattern was messier. The fossil record from the Karoo Basin in South Africa, which preserves the best record of Permian land vertebrates anywhere, shows that a major extinction had already hit terrestrial animals around 260 million years ago, during the mid-Permian Capitanian stage. That earlier event wiped out 74 to 80 percent of land-vertebrate genera in the region, thinning the roster well before the end-Permian blow.21PubMed Central. When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa Among the groups that made it across the Permian-Triassic boundary, the story was less one of sudden annihilation and more of rapid turnover, with bursts of extinction and origination in quick succession.22Palaeontology. Amniotes through major biological crises: faunal turnover among Parareptiles and the end‐Permian mass extinction
The Aftermath and the World of Lystrosaurus
What came after the extinction was in some ways as strange as the event itself. Early Triassic ecosystems were dominated by a handful of “disaster taxa,” species that thrived in the stripped-down, low-competition world left behind. On land, the most famous example is Lystrosaurus, a stocky, dog-sized herbivore related to modern mammals’ distant ancestors. It became so overwhelmingly common that it accounts for roughly 70 percent of individual fossils found in the extinction’s aftermath.23PubMed Central. Evidence from South Africa for a protracted end-Permian extinction on land Intriguingly, Lystrosaurus did not just boom after the extinction. Its abundance had already been climbing in the latest Permian, comprising about 54 percent of specimens before the main die-off, suggesting it was pre-adapted to deteriorating conditions rather than merely lucky.24PubMed Central. Evidence from South Africa for a protracted end-Permian extinction on land Early Triassic terrestrial communities showed a dramatic drop in ecological evenness, the sign of a world where a few generalists monopolized resources.25PubMed Central. Delayed recovery of non-marine tetrapods after the end-Permian mass extinction tracks global carbon cycle
Recovery was painfully slow. Environmental instability persisted throughout the Early Triassic, with recurring episodes of warming, anoxia, and carbon-cycle disruption that triggered additional smaller extinction events, repeatedly suppressing or even resetting recovery.26Nature. The timing and nature of marine ecosystem recovery following the Permian-Triassic mass extinction One of the starkest indicators is the coal gap. Early Triassic coals are completely absent from the global rock record, and coals do not reappear until the Middle Triassic, roughly 7 million years after the extinction. It took about 20 million years for peat-forming plant communities to return to their pre-extinction diversity and thickness.27Geological Society of America Bulletin. Global coal gap between Permian-Triassic extinction and Middle Triassic recovery of peat-forming plants A planet without coal-forming wetlands is a planet without lush, deeply rooted forest ecosystems. For millions of years, the continents were barren in a way that has no modern comparison.
The Lilliput Effect
Animals that survived did not just become rarer. They became smaller. Body fossils and trace fossils from the earliest Triassic are dramatically reduced in size compared to both older and younger intervals. The shrinkage was sharpest right at the boundary, in the first few hundred thousand years after the extinction, when surviving species and newly appearing ones alike were tiny relative to their later descendants.28Palaeogeography, Palaeoclimatology, Palaeoecology. The Lilliput effect in the aftermath of the end-Permian extinction event Detailed measurements of brachiopod and gastropod lineages that crossed the boundary show statistically significant drops in shell size, confirming that the Lilliput effect was not just an artifact of sampling but a real biological response.29Palaeogeography, Palaeoclimatology, Palaeoecology. Changes in size and growth rate of ‘Lilliput’ animals in the earliest Triassic Marine and terrestrial communities were affected similarly. Pre-extinction body sizes were not commonly seen again until at least the Middle Triassic, millions of years later.
Why did survivors shrink? Smaller bodies need less oxygen and fewer calories, both of which were in desperately short supply. In hot, oxygen-poor water, a small shell is easier to sustain than a large one. The Lilliput effect is essentially the biosphere’s emergency setting: when resources collapse, natural selection ruthlessly favors the smallest viable body plan.
Methane, Nickel, and Hidden Amplifiers
The Siberian Traps did not just pump out CO₂. The eruptions also released enormous quantities of nickel, which washed into the oceans and accumulated in sediments. Nickel is a key nutrient for methane-producing microorganisms (methanogens), and a sharp spike in nickel concentrations at the extinction horizon likely fueled a methanogenic bloom. That bloom would have poured additional methane, a potent greenhouse gas, into the atmosphere, amplifying the warming already driven by volcanic CO₂.30PubMed Central. Methanogenic burst in the end-Permian carbon cycle This kind of cascading feedback, where one volcanic product unlocks a biological process that worsens the original problem, helps explain why the crisis spiraled so far beyond what volcanic CO₂ alone might have caused.
An Uncomfortable Modern Parallel
Researchers have drawn cautious comparisons between the end-Permian crisis and modern ocean changes. The combination of warming, acidification, and expanding oxygen-minimum zones that characterizes today’s oceans echoes the same trio of stresses that devastated Permian seas. A review in the Annual Review of Earth and Planetary Sciences concluded that the end-Permian extinction may serve as an important ancient analog for twenty-first-century oceans.31Annual Review of Earth and Planetary Sciences. End-Permian Mass Extinction in the Oceans: An Ancient Analog for the Twenty-First Century? The comparison has limits. Modern carbon emissions are faster in rate but far smaller in total volume so far, and they have been sustained for only a couple of centuries rather than tens of millennia. No one is arguing that a full replay of the Great Dying is imminent. But the mechanistic parallels, particularly the sensitivity of marine organisms to simultaneous warming, deoxygenation, and pH decline, are close enough to make paleontologists uncomfortable. The end-Permian record shows what happens when those stresses compound over geological time, and the direction of modern trends matches the opening chapters of that story.