The Permian–Triassic extinction event, commonly known as the Great Dying, occurred at the boundary between the Permian and Triassic geologic periods, marking the end of the Paleozoic era and the beginning of the Mesozoic era. This event is Earth's most severe known extinction, with the loss of 57% of biological families, 62% of genera, 81% of marine species, and 70% of terrestrial vertebrate species. It also caused the greatest known mass extinction of insects. This event is the most extreme of the "Big Five" mass extinctions during the Phanerozoic eon. Evidence suggests one to three distinct phases of extinction, with the major marine extinction occurring over a 60,000- to 100,000-year period around 251.902 million years ago. There is debate about whether land extinctions occurred at the same time as the main marine extinction.
The leading scientific explanation for this extinction is the massive volcanic eruptions that formed the Siberian Traps. These eruptions released large amounts of sulfur dioxide and carbon dioxide, leading to oxygen-starved, sulfurous oceans, higher global temperatures, and more acidic oceans. Atmospheric carbon dioxide levels increased from about 400 ppm to 2,500 ppm, with 3,900 to 12,000 gigatonnes of carbon added to the ocean-atmosphere system during this time.
Other possible contributing factors include carbon dioxide emissions from burning oil and coal deposits caused by the eruptions, methane emissions from the breakdown of methane clathrates, methane released by new types of methane-producing microbes fed by minerals from the eruptions, stronger and longer El Niño events, and an extraterrestrial impact that created the Araguainha crater. This impact may have released methane and damaged the ozone layer, increasing exposure to solar radiation.
Dating
Scientists used to believe that rock layers from the time of the Permian–Triassic boundary were too few and incomplete to study in detail. Now, scientists can date the extinction event with great accuracy. Using uranium-lead dating of zircon crystals from five volcanic ash layers in Meishan, China, researchers created a detailed timeline for the extinction. This timeline helps scientists study how changes in the environment, the carbon cycle, and life on Earth were connected over thousands of years. The first appearance of the conodont Hindeodus parvus is used to mark the Permian–Triassic boundary in rock layers.
The extinction event happened between 251.941 ± 0.037 and 251.880 ± 0.031 million years ago, lasting about 60,000 ± 48,000 years. A sudden drop in the ratio of carbon-13 to carbon-12 in rocks from this time is linked to the extinction. This drop, called a negative carbon isotope excursion, was 4–7% in size and lasted about 500,000 years. However, it is hard to measure exactly because some rocks changed over time.
Evidence suggests Earth’s temperature rose by 8 °C (14 °F), and carbon dioxide levels reached 2,500 ppm. For comparison, carbon dioxide levels before the Industrial Revolution were 280 ppm, and today they are about 426 ppm. Scientists also found signs of increased ultraviolet radiation, which caused changes in plant spores.
Some studies suggest that the Permian–Triassic boundary is marked by a sudden increase in fungi, which may have fed on dead plants and animals. This "fungal spike" has been used to identify the boundary in rocks that cannot be dated using other methods. However, scientists have questioned this idea. For example, some argue that the most common fungal spore, Reduviasporonites, might actually be a type of algae, and the spike did not appear globally or always match the boundary. Newer chemical evidence supports a fungal origin for Reduviasporonites, reducing some of these concerns.
Scientists are still unsure about the exact timing and duration of the extinction. Some evidence suggests the extinction happened in one major event, while other studies found two separate extinction waves. For example, in Meishan, China, most extinctions seem to have happened around one peak. However, in other areas, like Liangfengya and Shangsi, two extinction events with different causes were found. Studies also show that different groups of animals and plants went extinct at different times. For example, ostracods and brachiopods went extinct about 670,000 to 1.17 million years apart.
Analysis of rocks from the Bowen Basin in Queensland shows that marine environments faced stress long before the end-Permian extinction, supporting the idea that the extinction was a slow process. Some studies suggest that the decline in marine life happened before the collapse of marine ecosystems.
There is debate about whether the extinction of land and sea life happened at the same time or at different times. In east Greenland, evidence shows that land and sea life declined together, though plants took longer to show the full effects. In South China, many rock layers show that land and sea extinctions happened at the same time. However, other studies suggest that land life began to decline 60,000 to 370,000 years before the marine extinction. Some evidence from Finnmark and Trøndelag shows that land plants changed before the major carbon isotope shift during the marine extinction. In the Karoo Basin, the boundary between two groups of fossils suggests that land life declined before the marine extinction. In South China, the Sunjiagou Formation also shows that land ecosystems declined before the marine crisis. Other research in tropical regions suggests that land life declined after the marine extinction.
The timing and causes of the Permian–Triassic extinction are complicated by the Capitanian extinction, which occurred earlier in the Permian period. Some extinctions once thought to happen at the Permian–Triassic boundary have been re-dated to the end of the Capitanian. It is unclear whether species that survived earlier extinctions had recovered enough to be considered separate from the Capitanian event. Some scientists believe the environmental changes caused a single, long extinction event, while others argue that two major extinction pulses happened 9.4 million years apart. According to this theory, the first pulse caused about 80% of marine species to go extinct, while the second pulse caused the final major extinction. For example, many dinocephalian genera and the Verbeekinidae family of foraminifera went extinct at the end of the Guadalupian epoch. The effects of this earlier extinction varied by location and group, with brachiopods and corals suffering severe losses.
Extinction patterns
Marine invertebrates faced the most severe losses during the Permian-Triassic (P–Tr) extinction, although earlier estimates of 90–96% marine species extinction were mixed up with the end-Capitanian mass extinction, which happened 7–10 million years earlier. Evidence of these losses was found in rock samples from south China near the P–Tr boundary. In these samples, 286 out of 329 marine invertebrate genera disappeared in the final two layers of sediment containing Permian conodonts. The drop in diversity was likely due to a sudden rise in extinctions, not a decrease in new species forming.
The extinction mainly affected organisms with calcium carbonate skeletons, especially those that relied on stable CO₂ levels to build them. These organisms were harmed by ocean acidification caused by rising atmospheric CO₂. Organisms using hemocyanin or hemoglobin to transport oxygen were more likely to survive than those using hemerythrin or oxygen diffusion. There is also evidence that being endemic (limited to a specific region) increased a taxon’s risk of extinction. Bivalve species that were endemic were more likely to go extinct than those found in many regions. Survival rates did not vary much based on latitude. Organisms living in areas less affected by global warming experienced fewer or delayed extinctions.
Among benthic (bottom-dwelling) organisms, the extinction event greatly increased background extinction rates, causing the greatest loss of species among those with high background extinction rates (which implies high turnover). The extinction rate for marine organisms was extremely high. Bioturbators (organisms that mix sediment) were severely affected, as shown by the loss of the mixed sediment layer in many marine environments during the end-Permian extinction.
Surviving marine invertebrate groups included articulate brachiopods (those with a hinge), which had slowly declined since the P–Tr extinction; the Ceratitida order of ammonites; and crinoids ("sea lilies"), which nearly went extinct but later became abundant. Groups with the highest survival rates generally had good control over circulation, complex gas exchange systems, and light calcification. Heavily calcified organisms with simple breathing systems suffered the most loss of species diversity. Among brachiopods, surviving species were typically small and rare compared to the diverse communities they once belonged to.
Conodonts suffered major losses in both the number of species and their physical diversity, though not as badly as during the Capitanian mass extinction.
Ammonoids, which had been declining for 30 million years since the Roadian (middle Permian), experienced a selective extinction 10 million years before the main event, at the end of the Capitanian stage. This earlier extinction greatly reduced the variety of ecological roles these organisms filled. Diversity and variety of forms fell further until the P–Tr boundary; the extinction at this time was non-selective, suggesting a sudden, catastrophic cause. During the Triassic, diversity increased rapidly, but variety of forms remained low. The range of possible shapes and structures among ammonoids became more limited as the Permian progressed. A few million years into the Triassic, the original range of ammonoid forms was reoccupied, but the distribution of these traits changed among different groups.
Ostracods experienced long-term changes in diversity before the P–Tr extinction, with many species vanishing suddenly. At least 74% of ostracods died during the P–Tr extinction itself.
Bryozoans had been declining throughout the Late Permian before suffering even greater losses during the P–Tr extinction, becoming the most severely affected group among lophophorates.
Deep-water sponges lost much of their diversity and saw a decrease in spicule size during the P–Tr extinction. Shallow-water sponges were less affected, with larger spicules and less loss of diversity compared to their deep-water counterparts.
Foraminifera faced a severe drop in diversity. Evidence from South China shows the extinction had two phases. Foraminifera diversity hotspots shifted to deeper waters during the P–Tr extinction. About 93% of late Permian foraminifera went extinct, with 50% of the Textulariina group, 92% of the Lagenida, 96% of the Fusulinida, and 100% of the Miliolida disappearing. Foraminifera with calcium carbonate shells had a 91% extinction rate. The survival of Lagenida compared to the complete extinction of Fusulinida may be due to Lagenida’s greater ability to live in different environments and their wider geographic range.
Cladodontomorph sharks likely survived by living in deep ocean refuges, as shown by the discovery of Early Cretaceous cladodontomorphs in deep, outer shelf environments. Ichthyosaurs, which evolved just before the P–Tr extinction, also survived.
The Lilliput effect, where species shrink during and after mass extinctions, was observed near the Permian-Triassic boundary in foraminifera, brachiopods, bivalves, and ostracods. While surviving gastropods were smaller than those that did not survive, it is unclear if the Lilliput effect applied to all gastropods. Some gastropod groups, called "Gulliver gastropods," grew larger after the extinction, showing the opposite of the Lilliput effect, known as the Brobdingnag effect.
The Permian had many insect and invertebrate species,
Biotic recovery
After the extinction event, the structure of Earth's ecosystems changed as surviving species adapted and new groups of life became more common. In the oceans, the "Paleozoic evolutionary fauna" declined, while the "modern evolutionary fauna" became more dominant. This shift began after the Capitanian mass extinction and reached its peak during the Late Jurassic. Typical ocean floor communities included bivalves, snails, sea urchins, and Malacostraca, while bony fish and marine reptiles thrived in open ocean areas. On land, dinosaurs and mammals first appeared during the Triassic period. The change in which species survived was partly due to the extinction event affecting some groups, like brachiopods, more than others, such as bivalves. Recovery also varied: some species went extinct later without diversifying again, while others became dominant over time.
Immediately after the end-Permian extinction, marine life was dominated by a few "disaster taxa," such as bivalves like Claraia and Unionites, conodonts like Clarkina and Hindeodus, brachiopods like Lingularia, and foraminifera like Earlandia and Rectocornuspira kalhori (sometimes classified as Ammodiscus). These communities had low diversity and showed little variation in species across different latitudes.
Scientists disagree on how quickly life recovered after the extinction. Some say it took 10 million years until the Middle Triassic, while others found evidence of faster recovery in specific areas. For example, marine life near Paris, Idaho, and in parts of China and Oman rebounded in about 1.3 million years. However, recovery varied by region, with some areas recovering faster than others. High-latitude ecosystems may have recovered more quickly due to increased productivity after the extinction. While taxonomic diversity returned quickly, functional ecological diversity took much longer to recover. Some studies suggest marine ecosystems were still recovering 50 million years later, during the latest Triassic.
Recovery speed also differed based on species type. Seafloor communities remained diverse for a long time, with epifaunal benthic species recovering slower than infaunal ones. In contrast, mobile organisms like ammonoids and conodonts recovered quickly, exceeding pre-extinction diversity within 2 million years. Recent research suggests recovery was driven by competition between species, with low competition slowing recovery in the Early Triassic and increased competition speeding it up later. Other factors, like repeated environmental stress and extreme heat, may have delayed recovery, especially for vulnerable species like skeletonized marine life.
By the Middle Triassic, most marine communities had recovered, but global marine diversity did not reach pre-extinction levels until the Middle Jurassic, about 75 million years after the extinction. Before the extinction, about two-thirds of marine animals were sessile, attached to the seafloor. During the Mesozoic, only about half were sessile, with more mobile species like snails, sea urchins, and crabs becoming common. After the extinction, complex ecosystems outnumbered simple ones by nearly three to one, leading to the Mesozoic Marine Revolution, marked by increased predation and durophagy.
Marine vertebrates recovered quickly, showing complex predator-prey relationships. Fossils from 5 million years after the extinction show vertebrates at the top of the food chain. Hybodont sharks had extremely fast tooth replacement, and ichthyopterygians grew rapidly in size. Bivalves became widespread in the Triassic, taking over niches previously held by brachiopods. While bivalves were once thought to outcompete brachiopods, this explanation remains debated.
Hypotheses about cause
Explaining events from 250 million years ago is very difficult because much of the evidence on land has been worn away or buried deep underground. The seafloor spreads and is recycled over 200 million years, leaving no useful clues beneath the ocean.
Scientists have still gathered strong evidence about the causes of the event. Some theories suggest sudden, large changes, while others suggest slower processes. These ideas are similar to those for another major extinction event, but scientists are not as certain about the causes of this one.
Any explanation for the event must address why certain organisms were most affected. These were organisms with shells made of calcium carbonate. The event lasted for 4 to 6 million years before life began to recover, and when recovery started, there was very little evidence of new minerals forming in living things, even though inorganic carbon was deposited.
The Siberian Traps, a massive volcanic area, erupted in a series of huge lava flows covering about 2,000,000 square kilometers—roughly the size of Saudi Arabia. These eruptions happened around the same time as the extinction event. Studies of the Siberian region show that the eruptions occurred in large, sudden bursts of magma, not in regular, steady flows.
The Siberian Traps caused one of the fastest increases in atmospheric carbon dioxide levels in Earth’s history. Scientists estimate that carbon dioxide emissions were five times faster than during a previous extinction event. Before the extinction, carbon dioxide levels were between 500 and 4,000 ppm, and after the event, they may have reached about 8,000 ppm. Another study suggests levels rose from 400 ppm to 2,500 ppm, with 3,900 to 12,000 gigatonnes of carbon added to the ocean and atmosphere. This led to extreme global warming, though some evidence shows a delay of 12,000 to 128,000 years between the rise in carbon dioxide and warming.
Before the extinction, global temperatures averaged about 18.2°C. They rose to as high as 35°C, with this extreme heat lasting up to 500,000 years. In the southern part of the supercontinent Gondwana, temperatures increased by about 10–14°C. In South China, ocean surface temperatures rose by about 8°C. In present-day Iran, tropical sea temperatures jumped from 27–33°C to over 35°C. These changes likely caused stronger El Niño events, making short-term climate changes more extreme.
High carbon dioxide levels lasted for a long time. The shape of the supercontinent Pangaea made it harder for Earth’s natural systems to remove carbon from the atmosphere. A 2020 study used a model to show how volcanic carbon dioxide emissions led to the extinction. Evidence also suggests that volcanic activity burned underground fossil fuel deposits, as shown by spikes in certain chemicals like mercury and carbon isotopes. Other signs, like unusual amounts of zinc from the Siberian Traps, support the link between volcanism and the extinction.
The Siberian Traps had features that made their effects even worse. The area had high levels of halogens, which destroy the ozone layer. Studies suggest that up to 70% of these halogens were released into the atmosphere, creating large amounts of hydrochloric acid and sulfur-rich gases. These gases formed dust clouds and acid rain, blocking sunlight and harming plants and ocean life. The sulfur also caused short-term global cooling, but these cold periods were too brief to explain the extinction.
The eruptions may have also caused acid rain, which could have killed land plants and marine organisms with calcium carbonate shells. While flood basalts usually produce lava that flows easily and doesn’t throw debris into the air, 20% of the Siberian Traps’ eruptions sent pyroclastic ash high into the atmosphere. This ash increased short-term cooling, but once it settled, carbon dioxide levels remained high, leading to long-term warming.
The Siberian Traps were located over layers of ancient carbonate, evaporite, and coal deposits. When volcanic activity heated these layers, they released large amounts of carbon dioxide and toxic gases. This likely worsened the extinction. The way the eruptions changed from lava flows to underground magma chambers may have released even more trapped carbon, matching the start of the extinction.
A 2011 study led by Stephen E. Grasby found evidence that volcanic activity caused coal deposits to ignite, possibly releasing over 3 trillion tons of carbon. Ash deposits near the Buchanan Lake Formation suggest that toxic elements from the eruptions entered water systems, harming ecosystems. However, some scientists argue that these ash layers may have come from wildfires unrelated to volcanic activity. A 2013 study by Q.Y. Yang estimated that the Siberian Traps released large amounts of carbon dioxide, carbon monoxide, hydrogen sulfide, and sulfur dioxide.
The way the Siberian Traps spread as underground magma chambers prolonged their warming effects, contributing to the severity of the extinction.
Comparison to present global warming
The PTME has been compared to today’s human-caused global warming and the Holocene extinction because all three involve quick releases of carbon dioxide. Although today’s greenhouse gas emissions are much higher than those during the PTME, the timing and pattern of emissions during the PTME are not fully understood. Scientists believe the PTME’s carbon release likely happened in short bursts over specific periods, not continuously. The rate of carbon release during these short bursts may have been similar to today’s human-caused emissions. Modern oceans, like those during the PTME, are experiencing lower pH and oxygen levels, which supports comparisons between past and present conditions. If carbon dioxide levels keep rising, another event similar to the PTME’s impact on marine life, called a bio-calcification crisis, may occur. Changes in how plants and insects interact during the PTME have also been studied as possible signs of future ecological changes. Because of these similarities, scientists warn that reducing carbon dioxide emissions is critical to avoiding a disaster like the PTME.
Today’s oceans are changing rapidly, with falling pH and oxygen levels, which strengthens the connection between the PTME and current conditions. As geologist Lee Kump explains:
The Permian-Triassic mass extinction shows the serious effects of fast carbon dioxide emissions. During the PTME, volcanic activity released huge amounts of CO₂, causing ocean acidification, low oxygen levels, and major ecological damage. Today, human activities are causing similar changes even faster. The geological record shows that once these critical thresholds are reached, the long-term effects on ecosystems can last millions of years.
If carbon dioxide levels continue to rise, another bio-calcification crisis may occur, as seen in the fossil record, which would severely harm modern marine ecosystems.