The Permian–Triassic extinction event, also called the Great Dying, was a major extinction that happened at the time when the Permian and Triassic geologic periods ended, marking the end of the Paleozoic era and the start of the Mesozoic era. It is Earth’s most severe known extinction, causing the loss of 57% of biological families, 62% of genera, 81% of marine species, and 70% of land vertebrate species. It also caused the greatest known loss of insect species. This event was the most severe of the "Big Five" mass extinctions in Earth’s history. Evidence suggests there were one to three separate phases of extinction, with the largest marine extinction occurring over 60,000 to 100,000 years around 251.902 million years ago. Scientists are still discussing whether the extinction on land happened at the same time as the main marine extinction.
Most scientists agree that the main cause of the extinction was 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 during this time, with 3,900 to 12,000 gigatonnes of carbon added to the ocean and atmosphere. Other possible factors include carbon dioxide released from burning oil and coal deposits, methane emissions from melting methane clathrates, methane produced by new types of microorganisms fed by minerals from the eruptions, stronger and longer El Niño events, and an extraterrestrial impact that created the Araguainha crater, releasing methane and damaging the ozone layer, which increased exposure to sunlight.
Dating
Previously, scientists believed that rock layers from the time of the Permian–Triassic boundary were too few or too damaged to study in detail. However, new methods now allow researchers to date the extinction with great accuracy. Using special dating techniques on volcanic ash layers from a key location in Meishan, China, scientists created a detailed timeline for the extinction. This timeline helps researchers explore how changes in Earth's environment, the carbon cycle, and life on Earth were connected over thousands of years. The first appearance of a tiny fossil called Hindeodus parvus is used to mark the Permian–Triassic boundary.
The extinction happened between 251.941 ± 0.037 and 251.880 ± 0.031 million years ago, lasting about 60,000 years. During this time, there was a sudden drop in the ratio of carbon-13 to carbon-12 in Earth's rocks, which is sometimes used to identify the Permian–Triassic boundary in rocks that cannot be dated using other methods. This change in carbon levels was large—4–7%—and lasted about 500,000 years. However, scientists find it hard to measure exactly because some rock layers changed over time.
Evidence also shows Earth’s temperature rose by about 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. There is also evidence that more ultraviolet radiation reached Earth, causing changes in plant spores.
Some scientists suggest that the Permian–Triassic boundary is marked by a sudden increase in fungi, both in the ocean and on land. This increase may have been caused by the large number of dead plants and animals that fungi fed on. This "fungal spike" has been used to identify the boundary in rocks that cannot be dated using other methods. However, others argue that the fungal spike may not be unique to the Permian–Triassic boundary and could have happened multiple times. Some research now supports that the most common fungal spore, Reduviasporonites, might have come from algae, not fungi.
There is still uncertainty about how long the extinction lasted and when different groups of life disappeared. Some studies suggest the extinction happened in a single event, while others find evidence of two separate waves. For example, in some areas, the extinction of certain creatures like ostracods and brachiopods happened millions of years apart. In the Bowen Basin of Queensland, signs of stress in ocean environments started long before the main extinction event. Some research suggests that the decline in ocean life happened before the collapse of entire ecosystems.
Scientists also debate whether the extinction of land and ocean life happened at the same time or at different times. Some evidence from Greenland shows that land and ocean life declined together, but plants took longer to show the full effects. In other areas, like South China, land and ocean extinctions appear to have happened together. However, other studies suggest that land life declined earlier than ocean life.
Studying the Permian–Triassic extinction is complicated by the Capitanian extinction, which happened earlier in the Permian period. Some extinctions once thought to have occurred at the Permian–Triassic boundary are now believed to have happened during the Capitanian event. It is unclear whether species that survived earlier extinctions fully recovered before the Permian–Triassic event. Some scientists argue that the environmental changes caused a single, long extinction event, while others believe it involved two major waves of extinction separated by millions of years. For example, many species of large marine animals died out near the end of the Guadalupian epoch, which was part of the Permian period.
Extinction patterns
During the P–Tr extinction, marine invertebrates experienced the most severe losses. Earlier estimates of 90–96% marine species extinction were incorrect because they mixed up the P–Tr event with the end-Capitanian extinction, which happened 7–10 million years earlier. Evidence from south China shows that 286 out of 329 marine invertebrate genera disappeared in the last two sedimentary layers containing Permian conodonts. The drop in diversity likely happened because of a sudden rise in extinctions, not because fewer new species formed.
Organisms with calcium carbonate skeletons, especially those needing stable CO₂ levels to build them, were most affected. These animals were harmed by ocean acidification caused by high atmospheric CO₂ levels. Animals using hemocyanin or hemoglobin to carry oxygen were more likely to survive than those using hemerythrin or oxygen diffusion. Species that lived only in specific areas (endemic) were more likely to go extinct than those found worldwide (cosmopolitan). Survival rates did not differ much between regions. Organisms in areas less affected by global warming had less severe or delayed extinctions.
Among benthic organisms, the extinction event greatly increased background extinction rates, causing the greatest losses for species that already had high background extinction rates. Marine extinction rates were extremely high. Bioturbators, which mix sediment, were severely affected, as shown by the loss of mixed sediment layers in many marine areas during the end-Permian extinction.
Surviving marine invertebrates included articulate brachiopods (with hinges), which had been declining since the P–Tr event; the Ceratitida order of ammonites; and crinoids ("sea lilies"), which nearly went extinct but later became diverse. Groups with high survival rates had good control over circulation, complex gas exchange systems, and light calcification. Heavily calcified species with simple breathing systems lost the most diversity. Surviving brachiopods were usually small and rare compared to their former diverse communities.
Conodonts suffered major losses in both species and body shape diversity, though not as badly as during the Capitanian extinction. Ammonoids, which had been declining for 30 million years, faced a major extinction 10 million years before the P–Tr event, reducing their variety of ecological roles. This early extinction was likely caused by environmental changes. Diversity and variety dropped further until the P–Tr event, which was not selective, suggesting a sudden cause. During the Triassic, diversity increased rapidly, but variety remained low. Ammonoids’ range of body forms became more limited as the Permian ended. By the early Triassic, their original range of forms was restored, but different groups now shared these traits.
Ostracods had long-term diversity changes before the P–Tr event, with most vanishing suddenly. At least 74% of ostracods died during the P–Tr event. Bryozoans had been declining throughout the Late Permian and suffered even greater losses during the P–Tr event, becoming the most affected lophophorate group.
Deep-water sponges lost diversity and had smaller spicules during the P–Tr event. Shallow-water sponges were less affected, with larger spicules and less loss of body shape diversity. Foraminifera faced a major diversity drop. Evidence from South China shows two extinction waves. Foraminifera hotspots shifted to deeper waters during the P–Tr event. About 93% of Permian foraminifera went extinct, including 100% of Miliolida, 96% of Fusulinida, 92% of Lagenida, and 50% of Textulariina. Foraminifera with calcium carbonate shells had a 91% extinction rate. Lagenides survived more than fusulinoidean fusulinides, possibly due to their broader environmental tolerance and wider geographic range.
Cladodontomorph sharks likely survived in deep ocean refuges, as shown by their presence in deep shelf environments in the Early Cretaceous. Ichthyosaurs, which evolved just before the P–Tr event, also survived.
The Lilliput effect, where species shrink during and after mass extinctions, was seen in foraminifera, brachiopods, bivalves, and ostracods. While surviving gastropods were smaller than those that died, it is unclear if the Lilliput effect applied to all gastropods. Some "Gulliver gastropods" grew larger, showing the opposite trend, called the Brobdingnag effect.
The Permian had many insect and invertebrate species, including the largest insects ever. The end-Permian event caused the largest known insect extinction, with eight to nine insect orders going extinct and ten others losing diversity. Palaeodictyopteroids declined in the mid-Permian, linked to changes in plant life. The worst decline happened in the Late Permian, likely not caused directly by weather-related plant changes. Some insect declines were due to biogeographic shifts rather than full extinctions.
Plant records from the Permian-Triassic boundary are limited, mostly based on pollen and spores. Plant changes varied by location and preservation. Plants are generally resistant to mass extinctions, with little impact on families. Plant diversity losses were less severe than marine animal losses. A 50% drop in species diversity may be due to fossilization processes. However, ecosystems changed greatly, with forests nearly disappearing. Dominant plant groups like Cordaites (gymnosperms) and Glossopteris (seed ferns) declined sharply. The extent of plant extinction remains debated.
The Glossopteris-dominated forests of high-latitude Gondwana collapsed in Australia 370,000 years before the P–Tr boundary. This collapse was less severe in western Gondwana.
Biotic recovery
After the extinction event, the structure of Earth's ecosystems changed as surviving species adapted and new ones appeared. In the ocean, the group of animals known as the "Paleozoic evolutionary fauna" decreased in numbers, while the "modern evolutionary fauna" became more common. This shift began with the Capitanian mass extinction and reached its peak during the Late Jurassic. Typical sea creatures included bivalves, snails, sea urchins, and Malacostraca, while bony fish and marine reptiles became more widespread in open ocean areas. On land, dinosaurs and mammals first appeared during the Triassic period. The change in species types was partly because some groups, like brachiopods, were more affected by the extinction than others, such as bivalves. However, recovery varied: some species went extinct millions of years later without regaining diversity, while others, like bivalves, became dominant over time.
Immediately after the end-Permian extinction, marine life was dominated by a few species called "disaster taxa," such as bivalves like Claraia and Unionites, conodonts like Clarkina and Hindeodus, and brachiopods like Lingularia. These ecosystems had low diversity and showed little variation in species across different latitudes.
Scientists disagree about how quickly life recovered after the extinction. Some say it took 10 million years until the Middle Triassic, but studies in places like Bear Lake County, Idaho, and areas in Nevada and China show that some ecosystems rebounded faster. For example, marine life in the Paris biota recovered in about 1.3 million years, and complex ecosystems in Italy and China showed signs of life less than a million years after the extinction. Differences in recovery speed suggest that some areas were less affected by the extinction, possibly due to environmental conditions like higher productivity in high-latitude regions. While species diversity increased quickly, it took much longer for ecosystems to return to their pre-extinction complexity. One study found that marine ecosystems were still recovering 50 million years later, during the latest Triassic.
Recovery speed also varied based on species type and lifestyle. Seafloor communities remained less diverse until the end of the Early Triassic, about 4 million years after the extinction. Epifaunal benthic organisms (those living on the seafloor) recovered slower than infaunal benthic organisms (those living within the seafloor). In contrast, mobile organisms like ammonoids and conodonts recovered faster, reaching pre-extinction levels within 2 million years. Recent research suggests that recovery was driven by competition between species, which influenced how quickly new species formed. In the Early Triassic, low competition slowed recovery, but by the Anisian period, increased competition accelerated biodiversity. Other factors, such as repeated environmental stress and extreme heat, may have delayed recovery, especially for species vulnerable to high carbon dioxide levels. Some areas with persistent environmental stress recovered more slowly, limiting the complexity of ecosystems until the Spathian period.
By the Middle Triassic, most marine communities had fully recovered, but global marine diversity reached pre-extinction levels only by 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), but during the Mesozoic, only about half were sessile, with more free-living species like snails, sea urchins, and crabs. Fossil evidence shows a decline in sessile suspension feeders like brachiopods and sea lilies and an increase in mobile species. After the extinction, complex ecosystems became more common than simple ones, leading to the Mesozoic Marine Revolution, marked by increased predation and durophagy (crushing prey).
Marine vertebrates recovered quickly, with evidence of predator-prey interactions appearing 5 million years after the extinction. Hybodont sharks replaced teeth rapidly, and ichthyopterygians (a group of marine reptiles) grew quickly in size. Bivalves expanded into many marine environments after the extinction, becoming more numerous and diverse in the Triassic. They took over niches previously filled by brachiopods, though earlier theories that bivalves outcompeted brachiopods may not fully explain this shift.
Hypotheses about cause
Explaining events that happened 250 million years ago is very difficult. Much of the evidence on land has been worn away or buried deep underground. The ocean floor spreads and re-forms over time, so there is little useful evidence left beneath the sea.
Scientists have found strong evidence about the causes of this event, and several theories have been proposed. These theories include both sudden, large-scale changes and slower, long-term processes. These ideas are similar to those studied for another major extinction event, but scientists are not as certain about the causes of this one.
Any theory about the cause must explain why certain organisms were affected more than others. For example, many animals with calcium carbonate skeletons died off. It also must explain why it took 4 to 6 million years before life began to recover. Additionally, even though inorganic carbon deposits formed after the event, very little biological material was preserved.
The Siberian Traps were among the largest volcanic events in Earth’s history. These eruptions covered an area about the size of Saudi Arabia, or 2,000,000 square kilometers. Scientists have studied the Siberian Traps and found that the eruptions happened in large bursts of magma, not in steady flows. These eruptions released huge amounts of carbon dioxide into the atmosphere. Scientists estimate that carbon dioxide levels rose five times faster than during a previous extinction event. One study suggests carbon dioxide levels increased from 500 to 4,000 ppm before the extinction to about 8,000 ppm afterward. Another study estimates that carbon dioxide levels rose from 400 ppm to 2,500 ppm, with 3,900 to 12,000 gigatonnes of carbon added to the ocean and atmosphere.
These high carbon dioxide levels caused extreme global warming. Some evidence suggests a delay of 12,000 to 128,000 years between the rise in carbon dioxide and the temperature increase. Scientists are still studying why this delay might have happened. During the extinction, global average surface temperatures rose from about 18.2°C to as high as 35°C. In some regions, such as Gondwana’s southern latitudes, temperatures increased by 10–14°C. In South China, ocean surface temperatures rose by about 8°C. In present-day Iran, tropical ocean temperatures jumped from 27–33°C to over 35°C. These changes likely caused stronger El Niño events, making climate patterns more unpredictable.
The high carbon dioxide levels lasted for a long time. At that time, the supercontinent Pangaea was positioned in a way that made the carbon cycle less effective at removing carbon from the atmosphere. A 2020 study used scientific models to show how volcanic carbon dioxide emissions caused the mass extinction. Evidence also suggests that volcanic activity burned underground fossil fuel deposits, as shown by spikes in mercury and carbon isotopes. Scientists found that the Siberian Traps released large amounts of isotopically light zinc, confirming that volcanism occurred at the same time as the extinction.
The Siberian Traps had unique features that made them even more dangerous. The area was rich in halogens, which can destroy the ozone layer. Scientists estimate that 70% of these halogens were released into the atmosphere, producing large amounts of hydrochloric acid and sulfur-rich gases. These gases formed dust clouds and acid rain, blocking sunlight and disrupting photosynthesis. This would have caused food chains to collapse. However, these cooling events were short-lived and likely did not directly cause the extinction.
The eruptions may have also caused acid rain, which could have harmed land plants and marine organisms with calcium carbonate shells. While flood basalts typically produce smooth lava flows, 20% of the Siberian Traps’ eruptions produced pyroclastic ash that reached high into the atmosphere. This ash increased short-term cooling. Once the ash settled, the excess carbon dioxide remained, leading to long-term warming.
The Siberian Traps were located over thick layers of ancient carbonate, evaporite, and coal deposits. When these rocks were heated by volcanic activity, they released large amounts of greenhouse gases and toxic chemicals. This likely worsened the extinction. The eruptions changed from producing flood basalts to forming sills, which released more trapped hydrocarbons. This change coincided with the start of the extinction and is linked to a major drop in carbon isotope levels.
Volcanic activity may have also caused coal to ignite, releasing massive amounts of methane and carbon dioxide. A 2011 study found evidence that volcanic eruptions caused coal beds to burn, possibly releasing over 3 trillion tons of carbon. Scientists discovered ash deposits in deep rock layers, suggesting that volcanic eruptions released toxic elements into water and air. However, some researchers argue that these ashes may have come from wildfires unrelated to coal combustion. A 2013 study estimated that the Siberian Traps released large amounts of carbon dioxide, carbon monoxide, hydrogen sulfide, and sulfur dioxide.
The way the Siberian Traps formed, with sills instead of flood basalts, prolonged their warming effects.
Comparison to present global warming
The Permian-Triassic Mass Extinction (PTME) has been compared to today’s human-caused global warming and the Holocene extinction because all three involve rapid increases in carbon dioxide levels. Although the current rate of greenhouse gas emissions is much higher than the rate during the PTME, scientists are unsure exactly when the greenhouse gas release happened during the PTME. It is likely that the release occurred in short, sudden bursts rather than continuously over time. During these bursts, the rate of carbon release may have been similar to today’s human-caused emissions.
Today’s oceans are experiencing similar changes to those during the PTME, including drops in pH and oxygen levels. These similarities have led scientists to compare modern human-caused environmental changes to those of the PTME. If carbon dioxide levels continue to rise, another event similar to the biocalcification crisis seen in the fossil record may occur, which could harm marine ecosystems. Changes in how plants and insects interact during the PTME have also been studied as possible signs of future ecological changes. Scientists warn that reducing carbon dioxide emissions is critical to avoiding a disaster similar to the PTME.
Just as during the PTME, today’s oceans are changing rapidly, with falling pH and oxygen levels. This connection is highlighted by geologist Lee Kump:
The Permian-Triassic mass extinction shows the dangers of rapid carbon dioxide emissions. Volcanic activity during the PTME released huge amounts of carbon dioxide, causing ocean acidification, low oxygen levels, and widespread loss of life. Today, human activities are causing similar changes, but even faster. The geological record shows that once these changes begin, ecosystems can suffer for millions of years.
If carbon dioxide levels continue to rise, another biocalcification crisis may occur, as seen in the fossil record. This would cause serious harm to modern marine ecosystems.