Permian-Triassic boundary at Frazer Beach, NSW

The Permian–Triassic (P–T, P–Tr) extinction event, also known as the Latest Permian extinction event, the End-Permian Extinction and colloquially as the Great Dying, formed the boundary between the

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Pale ...

and

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

geologic periods, as well as between the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

and

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Creta ...

eras, approximately 251.9 million years ago. It is the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

's most severe known extinction event, with the

extinction Extinction is the termination of a kind of organism or of a group of kinds ( taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed ...

of 57% of biological families, 83% of

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...

, 81% of marine

species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...

and 70% of

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...

species. It was the largest known mass extinction of

insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs ...

. There is evidence for one to three distinct pulses, or phases, of extinction. The scientific consensus is that the main cause of extinction was the large amount of

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

emitted by the volcanic eruptions that created the Siberian Traps, which elevated global temperatures, and in the oceans led to widespread

anoxia The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of di ...

and acidification. Proposed contributing factors include: the emission of much additional carbon dioxide from the thermal decomposition of

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

deposits, including oil and coal, triggered by the eruptions; and emissions of

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ear ...

by novel

methanogen Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain Archaea. All known methanogens are members of the archaeal phylum Euryarchaeota. Methanogens ar ...

ic microorganisms, perhaps nourished by minerals dispersed in the eruptions. The speed of recovery from the extinction is disputed. Some scientists estimate that it took 10 million years (until the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma ...

), due both to the severity of the extinction and because grim conditions returned periodically for another 5 million years, causing further extinction events, such as the Smithian-Spathian boundary extinction. However, studies in

Bear Lake County Bear Lake County is a county in the U.S. state of Idaho. As of the 2020 United States Census the county had a population of 6,372. The county seat is Paris, and Montpelier is the largest city. The county is named after Bear Lake, a large ...

, near Paris, Idaho, and nearby sites in Idaho and Nevada showed a relatively quick rebound in a localized

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a ...

marine ecosystem, taking around 3 million years to recover, while an unusually diverse and complex ichnobiota is known from Italy less than a million years after the end-Permian extinction, suggesting that the impact of the extinction may have been felt less severely in some areas than in others. Differential environmental stress and instability following the extinction event has been theorised as an explanation for the disparity in the pace of biotic recovery between different regions and environments.

Dating

Previously, it was thought that rock sequences spanning the Permian–Triassic boundary were too few and contained too many gaps for scientists to reliably determine its details. However, it is now possible to date the extinction with millennial precision. U–Pb

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of th ...

dates from five volcanic ash beds from the Global Stratotype Section and Point for the Permian–Triassic boundary at

Meishan Meishan (; Sichuanese Pinyin: Mi2san1; local pronunciation: ; ), formerly known as Meizhou () or Qingzhou (), is a prefecture-level city with 2,955,219 inhabitants as of 2020 census whom 1,232,648 lived in the built-up (or metro) area made of t ...

, China, establish a high-resolution age model for the extinction – allowing exploration of the links between global environmental perturbation,

carbon cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major componen ...

disruption, mass extinction, and recovery at millennial timescales. The extinction occurred between and years ago, a duration of 60 ± 48 thousand years. A large (approximately 0.9%), abrupt global decrease in the

ratio In mathematics, a ratio shows how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8:6, which is equivalent to the ...

of the stable isotope carbon-13 to that of carbon-12 coincides with this extinction, and is sometimes used to identify the Permian–Triassic boundary in rocks that are unsuitable for

radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...

. Further evidence for environmental change around the P–Tr boundary suggests an rise in temperature, and an increase in levels by (for comparison, the concentration immediately before the

Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...

was , and the amount today is about 415 ppm). There is also evidence of increased ultraviolet radiation reaching the earth, causing the

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, m ...

of plant spores. It has been suggested that the Permian–Triassic boundary is associated with a sharp increase in the abundance of marine and terrestrial

fungi A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...

, caused by the sharp increase in the amount of dead plants and animals fed upon by the fungi. For a while this "fungal spike" was used by some paleontologists to identify the Permian–Triassic boundary in rocks that are unsuitable for radiometric dating or have a lack of suitable index fossils, but even the proposers of the fungal spike hypothesis pointed out that "fungal spikes" may have been a repeating phenomenon created by the post-extinction ecosystem during the earliest Triassic. The very idea of a fungal spike has been criticized on several grounds, including: ''

Reduviasporonites Reduviasporonites or Tympanicysta are palynomorphs — microfossils which appear to be fungal or algal cells or spores. They were first described from specimens found in the Flowerpot Formation by L. R. Wilson in 1962. That first paper conjectu ...

'', the most common supposed fungal spore, may be a fossilized

alga Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from u ...

; the spike did not appear worldwide; and in many places it did not fall on the Permian–Triassic boundary. The reduviasporonites may even represent a transition to a lake-dominated Triassic world rather than an earliest Triassic zone of death and decay in some terrestrial fossil beds. Newer chemical evidence agrees better with a fungal origin for ''Reduviasporonites'', diluting these critiques. Uncertainty exists regarding the duration of the overall extinction and about the timing and duration of various groups' extinctions within the greater process. Some evidence suggests that there were multiple extinction pulses or that the extinction was long and spread out over a few million years, with a sharp peak in the last million years of the Permian. Statistical analyses of some highly fossiliferous

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

in Meishan,

Zhejiang Zhejiang ( or , ; , also romanized as Chekiang) is an eastern, coastal province of the People's Republic of China. Its capital and largest city is Hangzhou, and other notable cities include Ningbo and Wenzhou. Zhejiang is bordered by ...

Province in southeastern China, suggest that the main extinction was clustered around one peak. Recent research shows that different groups became extinct at different times; for example, while difficult to date absolutely, ostracod and

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, ...

extinctions were separated by around 670,000 to 1.17 million years. In a well-preserved sequence in east

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is ...

, the decline of animal life is concentrated in a period approximately 10,000 to 60,000 years long, with plants taking an additional several hundred thousand years to show the full impact of the event. Palaeoenvironmental analysis of Lopingian strata in the Bowen Basin of

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...

indicates numerous intermittent periods of environmental stress from the middle to late Lopingian leading up to the end-Permian extinction proper. An older theory, still supported in some recent papers, is that there were two major extinction pulses 9.4 million years apart, separated by a period of extinctions well above the background level, and that the final extinction killed off only about 80% of marine species alive at that time while the other losses occurred during the first pulse or the interval between pulses. According to this theory one of these extinction pulses occurred at the end of the Guadalupian epoch of the Permian. For example, all dinocephalian genera died out at the end of the Guadalupian, as did the

Verbeekinidae Verbeekinidae are a family of large fusulinaceans characterized by subspherical, planispirally coiled tests and a long coiling axis. The wall is composed of a dense outer tectum and inner alveolar keriotheca. They are most prominent in Japan and S ...

, a family of large-size fusuline

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

. The impact of the

end-Guadalupian extinction The Capitanian mass extinction event, also known as the end-Guadalupian extinction event or the pre-Lopingian crisis was an extinction event that predated the end-Permian extinction event and occurred around 260 million years ago during a period ...

on marine organisms appears to have varied between locations and between taxonomic groups –

s and

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and secre ...

s had severe losses. Studies of the timing and causes of the Permian-Triassic extinction are complicated by the often-overlooked Capitanian extinction (also called the ''Guadalupian extinction''), just one of perhaps two mass extinctions in the late

that closely preceded the Permian-Triassic event. In short, when the Permian-Triassic starts it is difficult to know whether the end-Capitanian had finished, depending on the factor considered. Some of the extinctions dated to the Permian-Triassic boundary have recently been redated to the end- Capitanian. Further, it is unclear whether some species who survived the prior extinction(s) had recovered well enough for their final demise in the Permian-Triassic event to be considered separate from Capitanian event. A minority point of view considers the sequence of environmental disasters to have effectively constituted a single, prolonged extinction event, perhaps depending on which species is considered.

Extinction patterns

Marine organisms

Marine invertebrates suffered the greatest losses during the P–Tr extinction. Evidence of this was found in samples from south China sections at the P–Tr boundary. Here, 286 out of 329 marine invertebrate genera disappear within the final two sedimentary zones containing

conodont Conodonts ( Greek ''kōnos'', " cone", + ''odont'', " tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, w ...

s from the Permian. The decrease in diversity was probably caused by a sharp increase in extinctions, rather than a decrease in

speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution withi ...

. The extinction primarily affected organisms with calcium carbonate skeletons, especially those reliant on stable CO₂ levels to produce their skeletons. These organisms were susceptible to the effects of the

ocean acidification Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxi ...

that resulted from increased atmospheric CO₂. Among

benthic organisms Benthos (), also known as benthon, is the community of organisms that live on, in, or near the bottom of a sea, river, lake, or stream, also known as the benthic zone.background extinction rates, and therefore caused maximum species loss to

taxa In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

that had a high background extinction rate (by implication, taxa with a high

turnover Turnover or turn over may refer to: Arts, entertainment, and media *''Turn Over'', a 1988 live album by Japanese band Show-Ya * Turnover (band), an American rock band *"Turnover", a song on Fugazi's 1990 album '' Repeater'' *''Turnover'', a Japane ...

). The extinction rate of marine organisms was catastrophic. Bioturbators were extremely severely affected, as evidenced by the loss of the sedimentary mixed layer in many marine facies during the end-Permian extinction. Surviving marine invertebrate groups included articulate brachiopods (those with a hinge), which had undergone a slow decline in numbers since the P–Tr extinction; the

Ceratitida Ceratitida is an order that contains almost all ammonoid cephalopod genera from the Triassic as well as ancestral forms from the Upper Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from t ...

order of

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttle ...

s; and

crinoid Crinoids are marine animals that make up the Class (biology), class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or coma ...

s ("sea lilies"), which very nearly became extinct but later became abundant and diverse. The groups with the highest survival rates generally had active control of

circulation Circulation may refer to: Science and technology * Atmospheric circulation, the large-scale movement of air * Circulation (physics), the path integral of the fluid velocity around a closed curve in a fluid flow field * Circulatory system, a bio ...

, elaborate gas exchange mechanisms, and light calcification; more heavily calcified organisms with simpler breathing apparatuses suffered the greatest loss of species diversity. In the case of the brachiopods, at least, surviving

were generally small, rare members of a formerly diverse community. The ammonoids, which had been in a long-term decline for the 30 million years since the Roadian (middle Permian), suffered a selective extinction pulse 10 million years before the main event, at the end of the Capitanian stage. In this preliminary extinction, which greatly reduced

disparity Disparity and disparities may refer to: in healthcare: * Health disparities in finance: * Income disparity between females and males. **Male–female income disparity in the United States **Income gender gap * Economic inequality * Income inequ ...

, or the range of different ecological guilds, environmental factors were apparently responsible. Diversity and disparity fell further until the P–Tr boundary; the extinction here (P–Tr) was non-selective, consistent with a catastrophic initiator. During the Triassic, diversity rose rapidly, but disparity remained low. The range of morphospace occupied by the ammonoids, that is, their range of possible forms, shapes or structures, became more restricted as the Permian progressed. A few million years into the Triassic, the original range of ammonoid structures was once again reoccupied, but the parameters were now shared differently among

clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term ...

Terrestrial invertebrates

The Permian had great diversity in insect and other invertebrate species, including the largest insects ever to have existed. The end-Permian is the largest known mass extinction of insects; according to some sources, it may well be the ''only'' mass extinction to significantly affect insect diversity. Eight or nine insect

orders Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

became extinct and ten more were greatly reduced in diversity. Palaeodictyopteroids (insects with piercing and sucking mouthparts) began to decline during the mid-Permian; these extinctions have been linked to a change in flora. The greatest decline occurred in the Late Permian and was probably not directly caused by weather-related floral transitions.

Terrestrial plants

The

geological record The geologic record in stratigraphy, paleontology and other natural sciences refers to the entirety of the layers of rock strata. That is, deposits laid down by volcanism or by deposition of sediment derived from weathering detritus (clays, sand ...

plants is sparse and based mostly on

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...

and

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

studies. Plants are relatively immune to mass extinction, with the impact of all the major mass extinctions "insignificant" at a family level. Even the reduction observed in species diversity (of 50%) may be mostly due to

taphonomic Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efrem ...

processes. However, a massive rearrangement of ecosystems does occur, with plant abundances and distributions changing profoundly and all the forests virtually disappearing. The dominant floral groups changed, with many groups of land plants entering abrupt decline, such as '' Cordaites'' (

gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...

s) and '' Glossopteris'' ( seed ferns); the Palaeozoic flora scarcely survived this extinction. The ''Glossopteris''-dominated flora that characterised high-latitude Gondwana collapsed in Australia around 370,000 years before the Permian-Triassic boundary, with this flora's collapse being less constrained in western Gondwana but still likely occurring a few hundred thousand years before the boundary. Palynological or pollen studies from East

of sedimentary rock strata laid down during the extinction period indicate dense gymnosperm

woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunlight and limited shade (see ...

s before the event. At the same time that marine

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

macrofauna declined, these large woodlands died out and were followed by a rise in diversity of smaller

herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition ...

plants including Lycopodiophyta, both Selaginellales and Isoetales. The ''Cordaites'' flora, which dominated the Angaran floristic realm corresponding to Siberia, collapsed over the course of the extinction. In the Kuznetsk Basin, the aridity-induced extinction of the regions's humid-adapted forest flora dominated by cordaitaleans occurred approximately 252.76 Ma, around 820,000 years before the end-Permian extinction in South China, suggesting that the end-Permian biotic catastrophe may have started earlier on land and that the ecological crisis may have been more gradual and asynchronous on land compared to its more abrupt onset in the marine realm. In South China, the subtropical Cathaysian gigantopterid dominated rainforests abruptly collapsed. The floral extinction in South China is associated with bacterial blooms in soil and nearby lacustrine ecosystems, with soil erosion resulting from the die-off of plants being their likely cause.

Terrestrial vertebrates

There is enough evidence to indicate that over two thirds of terrestrial labyrinthodont amphibians,

sauropsid Sauropsida ("lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia. Sauropsida is the sister taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early s ...

("reptile") and therapsid ("proto-mammal")

became extinct. Large

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthp ...

s suffered the heaviest losses. All Permian anapsid reptiles died out except the procolophonids (although testudines have ''morphologically''-anapsid skulls, they are now thought to have separately evolved from diapsid ancestors). Pelycosaurs died out before the end of the Permian. Too few Permian diapsid fossils have been found to support any conclusion about the effect of the Permian extinction on

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ...

s (the "reptile" group from which lizards, snakes, crocodilians, and

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s (including birds) evolved). The groups that survived suffered extremely heavy losses of species and some terrestrial vertebrate groups very nearly became extinct at the end of the Permian. Some of the surviving groups did not persist for long past this period, but others that barely survived went on to produce diverse and long-lasting lineages. However, it took 30million years for the terrestrial vertebrate fauna to fully recover both numerically and ecologically. It is difficult to analyze extinction and survival rates of land organisms in detail because few terrestrial fossil beds span the Permian–Triassic boundary. The best-known record of

changes across the Permian–Triassic boundary occurs in the Karoo Supergroup of

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring count ...

, but statistical analyses have so far not produced clear conclusions.

Biotic recovery

In the wake of the extinction event, the ecological structure of present-day biosphere evolved from the stock of surviving taxa. In the sea, the "Modern Evolutionary Fauna" became dominant over elements of the "Palaeozoic Evolutionary Fauna". Typical taxa of shelly benthic faunas were now bivalves,

snails A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Ga ...

, sea urchins and

Malacostraca Malacostraca (from New Latin; ) is the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobs ...

, whereas bony fishes and marine reptiles diversified in the

pelagic zone The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

. On land,

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

and

mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...

arose in the course of the

. The profound change in the taxonomic composition was partly a result of the selectivity of the extinction event, which affected some taxa (e.g., brachiopods) more severely than others (e.g., bivalves). However, recovery was also differential between taxa. Some survivors became extinct some million years after the extinction event without having rediversified ( dead clade walking, e.g. the snail family Bellerophontidae), whereas others rose to dominance over geologic times (e.g., bivalves).

Marine ecosystems

Marine post-extinction faunas were mostly species-poor and dominated by few disaster species such as the bivalves ''Claraia'' and ''Unionites''. Seafloor communities maintained a comparatively low diversity until the end of the Early Triassic, approximately 4 million years after the extinction event. This slow recovery stands in remarkable contrast with the quick recovery seen in nektonic organisms such as ammonoids, which exceeded pre-extinction diversities already two million years after the crisis. The relative delay in the recovery of benthic organisms has been attributed to widespread anoxia, but high abundances of benthic species contradict this explanation. More recent work suggests that the pace of recovery was intrinsically driven by the intensity of competition among species, which drives rates of niche differentiation and

. Accordingly, low levels of interspecific competition in seafloor communities that are dominated by primary consumers correspond to slow rates of diversification and high levels of interspecific competition among nektonic secondary and tertiary consumers to high diversification rates. Other studies point to the recurrent episodes of extremely hot climatic conditions during the Early Triassic for the delayed recovery of oceanic life. A 2019 study attributed the dissimilarity of recovery times between different ecological communities to differences in local environmental stress during the biotic recovery interval, with regions experiencing persistent environmental stress post-extinction recovering more slowly. Whereas most marine communities were fully recovered by the Middle Triassic, global marine diversity reached pre-extinction values no earlier than the Middle Jurassic, approximately 75 million years after the extinction event. Crinoïde Carbonifère 8127

Prior to the extinction, about two-thirds of marine animals were sessile and attached to the seafloor. During the Mesozoic, only about half of the marine animals were sessile while the rest were free-living. Analysis of marine fossils from the period indicated a decrease in the abundance of sessile epifaunal suspension feeders such as

s and sea lilies and an increase in more complex mobile species such as

snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class G ...

s, sea urchins and crabs. Before the Permian mass extinction event, both complex and simple marine ecosystems were equally common. After the recovery from the mass extinction, the complex communities outnumbered the simple communities by nearly three to one, and the increase in predation pressure led to the Mesozoic Marine Revolution. Bivalves were fairly rare before the P–Tr extinction but became numerous and diverse in the Triassic, taking over niches that were filled primarily by brachiopods before the mass extinction event, and one group, the rudist clams, became the

's main reef-builders. Some researchers think the change was attributable not only to the end-Permian extinction but also the ecological restructuring that began as a result of the Capitanian extinction.

Crinoid Crinoids are marine animals that make up the Class (biology), class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or coma ...

s ("sea lilies") suffered a selective extinction, resulting in a decrease in the variety of their forms. Their ensuing adaptive radiation was brisk, and resulted in forms possessing flexible arms becoming widespread;

motility Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...

, predominantly a response to predation pressure, also became far more prevalent. Microbial-metazoan reefs dominated surviving communities in the immediate wake of the mass extinction. Metazoan-built reefs reemerged during the Olenekian, mainly being composed of sponge biostrome and bivalve builups. "''Tubiphytes''"-dominated reefs appeared at the end of the Olenekian, representing the earliest platform-margin reefs of the Triassic, though they did not become abundant until the late Anisian, when reefs' species richness increased. The first scleractinian corals appear in the late Anisian as well, although they would not become the dominant reef builders until the end of the Triassic period.

Terrestrial plants

The proto-recovery of terrestrial floras took place from a few tens of thousands of years after the end-Permian extinction to around 350,000 years after it, with the exact timeline varying by region. Dominant

genera were replaced post-boundary by

lycophytes The lycophytes, when broadly circumscribed, are a vascular plant (tracheophyte) subgroup of the kingdom Plantae. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldest ...

extant lycophytes are recolonizers of disturbed areas. The particular post-extinction dominance of lycophytes, which were well adapted for coastal environments, can be explained in part by global marine transgressions during the Early Triassic. The worldwide recovery of gymnosperm forests took approximately 4–5 million years. However, this trend of prolonged lycophyte dominance during the Early Triassic was not universal, as evidenced by the much more rapid recovery of gymnosperms in certain regions, and floral recovery likely didn't follow a congruent, globally universal trend but instead varied by region according to local environmental conditions. In East Greenland, lycophytes replaced gymnosperms as the dominant plants. Later, other groups of

s again become dominant but again suffered major die-offs. These cyclical flora shifts occurred a few times over the course of the extinction period and afterward. These fluctuations of the dominant flora between woody and

taxa indicate chronic environmental stress resulting in a loss of most large woodland plant species. The successions and extinctions of plant communities do not coincide with the shift in values but occurred many years after. In what is now the Barents Sea of the coast of Norway, the post-extinction fauna is dominated by pteridophytes and lycopods, which were suited for primary succession and recolonisation of devastated areas, although gymnosperms made a rapid recovery, with the lycopod dominated flora not persisting across most of the Early Triassic as postulated in other regions. In Europe and North China, the interval of recovery was dominated by the lycopsid ''Pleuromeia'', an opportunistic pioneer plant that filled ecological vacancies until other plants were able to expand out of refugia and recolonise the land. Conifers became common by the early Anisian, while pteridosperms and cycadophytes only fully recovered by the late Anisian. In southwestern Gondwana, the post-extinction flora was dominated by bennettitaleans and cycads, with memers of Peltaspermales, Ginkgoales, and Umkomasiales being less common constituents of this flora. Around the Induan-Olenekian boundary, as palaeocommunities recovered, a new ''Dicroidium'' flora was established, in which Umkomasiales continued to be prominent and in which Equisetales and Cycadales were subordinate forms. The ''Dicroidium'' flora further diversified in the Anisian to its peak, wherein Umkomasiales and Ginkgoales constituted most of the tree canopy and Peltaspermales, Petriellales, Cycadales, Umkomasiales, Gnetales, Equisetales, and Dipteridaceae dominated the understory. The gigantopterid-dominated forests of South China were replaced by low-lying herbaceous vegetation dominated by the isoetalean '' Tomiostrobus'' following the collapse of the former. In contrast to the highly biodiverse gigantopterid rainforests, the post-extinction landscape of South China was near-barren and had vastly lower diversity.

Coal gap

coal Coal is a combustible black or brownish-black sedimentary rock, formed as stratum, rock strata called coal seams. Coal is mostly carbon with variable amounts of other Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen ...

deposits are known from the Early Triassic, and those in the Middle Triassic are thin and low-grade. This "coal gap" has been explained in many ways. It has been suggested that new, more aggressive fungi, insects, and vertebrates evolved and killed vast numbers of trees. These

decomposer Decomposers are organisms that break down dead or decaying organisms; they carry out decomposition, a process possible by only certain kingdoms, such as fungi. Like herbivores and predators, decomposers are heterotrophic, meaning that they use ...

s themselves suffered heavy losses of species during the extinction and are not considered a likely cause of the coal gap. It could simply be that all coal-forming plants were rendered extinct by the P–Tr extinction and that it took 10 million years for a new suite of plants to adapt to the moist, acid conditions of

peat Peat (), also known as turf (), is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem covers and is the most efficien ...

bogs. Abiotic factors (factors not caused by

organism In biology, an organism () is any life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), taxonomy into groups such as Multicellular o ...

s), such as decreased rainfall or increased input of clastic sediments, may also be to blame. On the other hand, the lack of coal may simply reflect the scarcity of all known

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

s from the Early Triassic. Coal-producing

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

s, rather than disappearing, may have moved to areas where we have no sedimentary record for the Early Triassic. For example, in eastern Australia a cold climate had been the norm for a long period, with a peat mire ecosystem adapted to these conditions. Approximately 95% of these peat-producing plants went ''locally'' extinct at the P–Tr boundary; coal deposits in Australia and Antarctica disappear significantly ''before'' the P–Tr boundary.

Terrestrial vertebrates

'' Lystrosaurus'', a pig-sized herbivorous dicynodont therapsid, constituted as much as 90% of some earliest Triassic land vertebrate fauna. Smaller carnivorous cynodont therapsids also survived, including the ancestors of

. In the

Karoo The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe !Orakobab or Khoemana word ''ǃ’Aukarob'' "Hardveld") is a semi- desert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its ...

region of southern

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

, the therocephalians ''

Tetracynodon ''Tetracynodon'' is an extinct genus of therocephalian. Fossils of ''Tetracynodon'' have been found in the Karoo Basin of South Africa. Two species are known: the type species ''T. tenuis'' from the Late Permian and the species ''T. darti'' ...

'', '' Moschorhinus'' and ''

Ictidosuchoides ''Ictidosuchoides'' is an extinct genus of ictidosuchid therocephalians. Fossils have been found from the Karoo Basin in South Africa. The genus is known to have been one of the few therocephalians to have survived the Permian-Triassic extinct ...

'' survived, but do not appear to have been abundant in the Triassic. In North China, tetrapod body and ichnofossils are extremely rare in Induan facies, but become more abundant in the Olenekian and Anisian, showing a biotic recovery of tetrapods synchronous with the decreasing aridity during the Olenekian and Anisian. Archosaurs (which included the ancestors of dinosaurs and

crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...

ns) were initially rarer than therapsids, but they began to displace therapsids in the mid-Triassic. In the mid to late Triassic, the

s evolved from one group of archosaurs, and went on to dominate terrestrial ecosystems during the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

and

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

. This "Triassic Takeover" may have contributed to the evolution of mammals by forcing the surviving therapsids and their mammaliform successors to live as small, mainly

nocturnal Nocturnality is an ethology, animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatures generally have ...

insectivore A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores wer ...

s; nocturnal life probably forced at least the mammaliforms to develop fur, better

hearing Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is audit ...

and higher

metabolic rate Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cel ...

s, while losing part of the differential color-sensitive retinal receptors reptilians and birds preserved. The archosaur dominance would end again due to the

Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden extinction event, mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million y ...

, after which both

birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

(only extant dinosaurs) and

(only extant synapsids) would diversify and share the world. Some temnospondyl amphibians made a relatively quick recovery, in spite of nearly becoming extinct. '' Mastodonsaurus'' and trematosaurians were the main aquatic and semiaquatic predators during most of the

, some preying on

tetrapod Tetrapods (; ) are four-limb (anatomy), limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant taxon, extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (p ...

s and others on fish. Land vertebrates took an unusually long time to recover from the P–Tr extinction; Palaeontologist Michael Benton estimated the recovery was not complete until after the extinction, i.e. not until the Late Triassic, when the first

had risen from bipedal archosaurian ancestors and the first

from small cynodont ancestors.

Terrestrial invertebrates

Most fossil insect groups found after the Permian–Triassic boundary differ significantly from those before: Of Paleozoic insect groups, only the

Glosselytrodea Glosselytrodea is an extinct order of insects, containing about thirty species. Its fossil record dates from the Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the ...

, Miomoptera, and Protorthoptera have been discovered in deposits from after the extinction. The caloneurodeans, monurans, paleodictyopteroids, protelytropterans, and protodonates became extinct by the end of the Permian. Though Triassic insects are very different from those of the Permian, a gap in the insect fossil record spans approximately 15 million years from the late Permian to early Triassic. In well-documented Late Triassic deposits, fossils overwhelmingly consist of modern fossil insect groups.

Hypotheses about cause

Pinpointing the exact causes of the Permian–Triassic extinction event is difficult, mostly because it occurred over 250 million years ago, and since then much of the evidence that would have pointed to the cause has been destroyed or is concealed deep within the Earth under many layers of rock. The

sea floor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

is completely recycled over around 200 million years by the ongoing process of

plate tectonics Plate tectonics (from the la, label= Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large t ...

and seafloor spreading, leaving no useful indications beneath the ocean. Yet, scientists have gathered significant evidence for causes, and several mechanisms have been proposed. The proposals include both catastrophic and gradual processes (similar to those theorized for the

). *The ''catastrophic'' group includes one or more large bolide impact events, increased

volcanism Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the Earth#Surface, surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the su ...

, and sudden release of methane from the seafloor, either due to dissociation of methane hydrate deposits or metabolism of organic carbon deposits by

ic microbes. *The ''gradual'' group includes sea level change, increasing hypoxia, and increasing

arid A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ...

ity. Any hypothesis about the cause must explain the selectivity of the event, which affected organisms with calcium carbonate skeletons most severely; the long period (4 to 6 million years) before recovery started, and the minimal extent of biological mineralization (despite

inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemis ...

carbonates being deposited) once the recovery began.

Volcanism

The final stages of the Permian had two

flood basalt A flood basalt (or plateau basalt) is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Many flood basalts have been attributed to the onset of a hotspot reac ...

events. A smaller one, the Emeishan Traps in China, occurred at the same time as the

pulse, in an area close to the equator at the time. The flood basalt eruptions that produced the Siberian Traps constituted one of the largest known volcanic events on Earth and covered over with lava. The date of the Siberian Traps eruptions and the extinction event are in good agreement. The Siberian Traps are underlain by thick sequences of Early-Mid

aged

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonat ...

and

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

deposits, as well as Carboniferous-Permian aged coal bearing clastic rocks. When heated, such as by

igneous intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s, these rocks are capable of emitting large amounts of greenhouse and toxic gases. The unique setting of the Siberian Traps over these deposits is likely the reason for the severity of the extinction. The timing of the change of the Siberian Traps from flood basalt dominated emplacement to sill dominated emplacement, the latter of which would have liberated the largest amounts of trapped hydrocarbon deposits, coincides with the onset of the main phase of the mass extinction and is linked to a major negative excursion. The Siberian Traps eruptions released sulphur-rich volatiles that caused dust clouds and the formation of acid

aerosols An aerosol is a suspension (chemistry), suspension of fine solid particles or liquid Drop (liquid), droplets in air or another gas. Aerosols can be natural or Human impact on the environment, anthropogenic. Examples of natural aerosols are fog o ...

, which would have blocked out sunlight and thus disrupted photosynthesis both on land and in the photic zone of the ocean, causing food chains to collapse. These volcanic outbursts of sulphur also induced brief but severe global cooling, leading to glacio-eustatic sea level fall. The eruptions may also have caused acid rain as the aerosols washed out of the atmosphere. That may have killed land plants and

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is es ...

s and

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cr ...

ic organisms which had calcium carbonate shells. The eruptions would also have emitted

, causing

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate variability and change, Climate change in a broader sense also includes ...

. When all of the dust clouds and aerosols washed out of the atmosphere, the excess carbon dioxide would have remained and the warming would have proceeded without any mitigating effects. The Siberian Traps had unusual features that made them even more dangerous. Pure flood basalts produce fluid, low-viscosity lava, and do not hurl debris into the atmosphere. It appears, however, that 20% of the output of the Siberian Traps eruptions was

pyroclastic Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...

(consisted of ash and other debris thrown high into the atmosphere), increasing the short-term cooling effect. The basalt lava erupted or intruded into

rocks and into sediments that were in the process of forming large coal beds, both of which would have emitted large amounts of carbon dioxide, leading to stronger global warming after the dust and

aerosol An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. Aerosols can be natural or anthropogenic. Examples of natural aerosols are fog or mist, dust, forest exudates, and geyser steam. Examples of ant ...

s settled. In addition, these volcanic eruptions released significant quantities of toxic mercury into the atmosphere and ocean, further contributing to large scale die-offs of terrestrial and marine life. In January 2011, a team, led by Stephen Grasby of the Geological Survey of Canada – Calgary, reported evidence that volcanism caused massive coal beds to ignite, possibly releasing more than 3 trillion tons of carbon. The team found ash deposits in deep rock layers near what is now the Buchanan Lake Formation. According to their article, "coal ash dispersed by the explosive Siberian Trap eruption would be expected to have an associated release of toxic elements in impacted water bodies where

fly ash Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK) plurale tantum: coal combustion residuals (CCRs)is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired ...

slurries developed. ... Mafic megascale eruptions are long-lived events that would allow significant build-up of global ash clouds." In a statement, Grasby said, "In addition to these volcanoes causing fires through coal, the ash it spewed was highly toxic and was released in the land and water, potentially contributing to the worst extinction event in earth history." In 2013, a team led by Q.Y. Yang reported the total amounts of important volatiles emitted from the Siberian Traps are * 8.5 × Tg CO, * 4.4 × Tg CO, * 7.0 × Tg HS, and * 6.8 × Tg SO. The data support a popular notion that the end-Permian mass extinction on the Earth was caused by the emission of enormous amounts of volatiles from the Siberian Traps into the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. ...

. In 2015, evidence and a timeline indicated the extinction was caused by events in the large igneous province of the Siberian Traps. Carbon dioxide levels prior to and after the eruptions are poorly constrained, but may have jumped from between 500 and 4000 prior to the extinction event to around 8000 after the extinction. In 2020 scientists reconstructed the mechanisms that led to the extinction event in a biogeochemical model, showed the consequences of the greenhouse effect on the marine environment and reported that the mass extinction can be traced back to volcanic CO emissions. Further evidence – based on paired coronene-mercury spikes – for a volcanic combustion cause of the mass extinction was published in 2020. CC-BY icon

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Methane clathrate gasification

Methane clathrates, also known as methane hydrates, consist of methane molecules trapped in cages of water molecules. The methane, produced by methanogens (microscopic single-celled organisms), has a about 6.0% below normal ( −6.0%). At the right combination of pressure and temperature, the methane is trapped in clathrates fairly close to the surface of

permafrost Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surfac ...

and, in much larger quantities, on continental shelves and the deeper seabed close to them. Oceanic methane hydrates are usually found buried in sediments where the seawater is at least deep. They can be found up to about below the sea floor, but usually only about below the sea floor. The release of methane from the clathrates has been considered as a cause because scientists have found worldwide evidence of a swift decrease of about 1% in the in

rocks from the end-Permian. This is the first, largest, and most rapid of a series of negative and positive excursions (decreases and increases in ) that continues until the

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass number ...

abruptly stabilised in the middle Triassic, followed soon afterwards by the recovery of calcifying life forms (organisms that use calcium carbonate to build hard parts such as shells). While a variety of factors may have contributed to this drop in the , a 2002 review found most of them to be insufficient to account fully for the observed amount: * Gases from volcanic eruptions have a about 0.5 to 0.8% below standard ( about −0.5 to −0.8%), but an assessment made in 1995 concluded that the amount required to produce a reduction of about 1.0% worldwide requires eruptions greater by orders of magnitude than any for which evidence has been found. (However, this analysis addressed only CO₂ produced by the magma itself, not from interactions with carbon bearing sediments, as later proposed.) * A reduction in organic activity would extract C more slowly from the environment and leave more of it to be incorporated into sediments, thus reducing the Biochemical processes preferentially use the lighter isotopes since chemical reactions are ultimately driven by electromagnetic forces between atoms and lighter isotopes respond more quickly to these forces, but a study of a smaller drop of 0.3 to 0.4% in ( −3 to −4 ‰) at the Paleocene-Eocene Thermal Maximum (PETM) concluded that even transferring all the organic

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

(in organisms, soils, and dissolved in the ocean) into sediments would be insufficient: Even such a large burial of material rich in C would not have produced the 'smaller' drop in the of the rocks around the PETM. * Buried sedimentary organic matter has a 2.0 to 2.5% below normal ( −2.0 to −2.5%). Theoretically, if the sea level fell sharply, shallow marine sediments would be exposed to oxidation. But 6500–8400 gigatons (1 gigaton =

metric ton The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...

s) of organic carbon would have to be oxidized and returned to the ocean-atmosphere system within less than a few hundred thousand years to reduce the by 1.0%, which is not thought to be a realistic possibility. Moreover, sea levels were rising rather than falling at the time of the extinction. * Rather than a sudden decline in sea level, intermittent periods of ocean-bottom hyperoxia and

(high-oxygen and low- or zero-oxygen conditions) may have caused the fluctuations in the Early Triassic; and global anoxia may have been responsible for the end-Permian blip. The continents of the end-Permian and early Triassic were more clustered in the tropics than they are now, and large tropical rivers would have dumped sediment into smaller, partially enclosed ocean basins at low latitudes. Such conditions favor oxic and anoxic episodes; oxic/anoxic conditions would result in a rapid release/burial, respectively, of large amounts of organic carbon, which has a low because biochemical processes use the lighter isotopes more. Preliminary abstract at That or another organic-based reason may have been responsible for both that and a late Proterozoic/Cambrian pattern of fluctuating Other hypotheses include mass oceanic poisoning, releasing vast amounts of CO, and a long-term reorganisation of the global carbon cycle. Prior to consideration of the inclusion of roasting carbonate sediments by volcanism, the only proposed mechanism sufficient to cause a global 1% reduction in the was the release of

from methane clathrates. Carbon-cycle models confirm that it would have had enough effect to produce the observed reduction. It was also suggested that a large-scale release of methane and other

greenhouse gas A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), met ...

es from the ocean into the atmosphere was connected to the anoxic events and euxinic (i.e. sulfidic) events at the time, with the exact mechanism compared to the 1986 Lake Nyos disaster The area covered by lava from the Siberian Traps eruptions is about twice as large as was originally thought, and most of the additional area was shallow sea at the time. The seabed probably contained methane hydrate deposits, and the lava caused the deposits to dissociate, releasing vast quantities of methane. A vast release of methane might cause significant global warming since methane is a very powerful

. Strong evidence suggests the global temperatures increased by about 6 °C (10.8 °F) near the equator and therefore by more at higher latitudes: a sharp decrease in oxygen isotope ratios (); the extinction of '' Glossopteris'' flora (''Glossopteris'' and plants that grew in the same areas), which needed a cold

climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologica ...

, with its replacement by floras typical of lower paleolatitudes. However, the pattern of isotope shifts expected to result from a massive release of methane does not match the patterns seen throughout the Early Triassic. Not only would such a cause require the release of five times as much methane as postulated for the PETM, but would it also have to be reburied at an unrealistically high rate to account for the rapid increases in the (episodes of high positive ) throughout the early Triassic before it was released several times again. As of 2022, latest research suggests that greenhouse gas release during the extinction event was dominated by volcanic carbon dioxide: while methane release had to have contributed, isotopic signatures show that thermogenic methane released from the Siberian Traps had consistently played a larger role than methane from clathrates and any other biogenic sources such as wetlands during the event.

Hypercapnia and acidification

Marine organisms are more sensitive to changes in (

) levels than terrestrial organisms for a variety of reasons. is 28 times more

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

in water than is oxygen. Marine animals normally function with lower concentrations of in their bodies than land animals, as the removal of in air-breathing animals is impeded by the need for the gas to pass through the respiratory system's

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...

s ( lungs' alveolus,

tracheae The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air- breathing animals with lungs. The trachea extends from the ...

, and the like), even when diffuses more easily than oxygen. In marine organisms, relatively modest but sustained increases in concentrations hamper the synthesis of

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

s, reduce fertilization rates, and produce deformities in calcareous hard parts. An analysis of marine fossils from the Permian's final Changhsingian stage found that marine organisms with a low tolerance for

hypercapnia Hypercapnia (from the Greek ''hyper'' = "above" or "too much" and ''kapnos'' = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous pr ...

(high concentration of

) had high extinction rates, and the most tolerant organisms had very slight losses. The most vulnerable marine organisms were those that produced calcareous hard parts (from calcium carbonate) and had low

s and weak

respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

s, notably

calcareous sponge The calcareous sponges of class Calcarea are members of the animal phylum Porifera, the cellular sponges. They are characterized by spicules made of calcium carbonate in the form of calcite or aragonite. While the spicules in most species hav ...

s, rugose and tabulate corals,

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scra ...

-depositing

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...

ns, and

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...

s; about 81% of such

became extinct. Close relatives without

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an a ...

hard parts suffered only minor losses, such as sea anemones, from which modern corals evolved. Animals with high metabolic rates, well-developed respiratory systems, and non-calcareous hard parts had negligible losses except for

s, in which 33% of genera died out. This pattern is also consistent with what is known about the effects of hypoxia, a shortage but not total absence of

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

. However, hypoxia cannot have been the only killing mechanism for marine organisms. Nearly all of the continental shelf waters would have had to become severely hypoxic to account for the magnitude of the extinction, but such a catastrophe would make it difficult to explain the very selective pattern of the extinction. Mathematical models of the Late Permian and Early Triassic atmospheres show a significant but protracted decline in atmospheric oxygen levels, with no acceleration near the P–Tr boundary. Minimum atmospheric oxygen levels in the Early Triassic are never less than present-day levels and so the decline in oxygen levels does not match the temporal pattern of the extinction. In addition, an increase in concentration is inevitably linked to

, consistent with the preferential extinction of heavily calcified taxa and other signals in the rock record that suggest a more acidic ocean. The decrease in ocean pH is calculated to be up to 0.7 units. Ocean acidification was most extreme at mid-latitudes, and the major marine transgression associated with the end-Permian extinction is believed to have devastated shallow shelf communities in conjunction with anoxia. Evidence from paralic facies spanning the Permian-Triassic boundary in western

Guizhou Guizhou (; formerly Kweichow) is a landlocked province in the southwest region of the People's Republic of China. Its capital and largest city is Guiyang, in the center of the province. Guizhou borders the autonomous region of Guangxi to t ...

and eastern

Yunnan Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the ...

, however, shows a local marine transgression dominated by carbonate deposition, suggesting that ocean acidification did not occur across the entire globe and was likely limited to certain regions of the world's oceans. On land, the increasing acidification of rainwater caused increased soil erosion as a result of the increased acidity of forest soils, evidenced by the increased influx of terrestrially derived organic sediments found in marine sedimentary deposits during the end-Permian extinction. A positive feedback loop further enhancing and prolonging soil acidification may have resulted from the decline of infaunal invertebrates like tubificids and chironomids, which remove acid metabolites from the soil. The increased abundance of vermiculitic clays in Shansi, South China coinciding with the Permian-Triassic boundary strongly suggests a sharp drop in soil pH causally related to volcanogenic emissions of carbon dioxide and sulphur dioxide.

Anoxia and euxinia

Evidence for widespread ocean

(severe deficiency of oxygen) and euxinia (presence of

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The und ...

) is found from the Late Permian to the Early Triassic. Throughout most of the Tethys and

Panthalassic Panthalassa, also known as the Panthalassic Ocean or Panthalassan Ocean (from Greek "all" and "sea"), was the superocean that surrounded the supercontinent Pangaea, the latest in a series of supercontinents in the history of Earth. During ...

Oceans, evidence for anoxia, including fine laminations in sediments, small pyrite framboids, high uranium/thorium ratios, and biomarkers for green sulfur bacteria, appear at the extinction event. However, evidence for anoxia precedes the extinction at some other sites, including Spiti,

India India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...

, China, Opal Creek,

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

, and Kap Stosch, Greenland. Biomarkers for green sulfur bacteria, such as isorenieratane, the diagenetic product of

isorenieratene Isorenieratene is a carotenoid light harvesting pigment with the chemical formula C40H48. Isorenieratene and its derivatives are useful to marine chemists studying the carbon cycle as biomarkers that indicate photic zone anoxia. Isorenieraten ...

, are widely used as indicators of photic zone euxinia because green sulfur

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

require both sunlight and hydrogen sulfide to survive. Their abundance in sediments from the P–T boundary indicates hydrogen sulfide was present even in shallow waters. The disproportionate extinction of high-latitude marine species provides further evidence for oxygen depletion as a killing mechanism; low-latitude species living in warmer, less oxygenated waters are naturally better adapted to lower levels of oxygen and are able to migrate to higher latitudes during periods of global warming, whereas high-latitude organisms are unable to escape from warming, hypoxic waters at the poles. This spread of toxic, oxygen-depleted water would have devastated marine life, causing widespread die-offs. Models of ocean chemistry suggest that anoxia and euxinia were closely associated with

(high levels of carbon dioxide). This suggests that poisoning from

, anoxia, and hypercapnia acted together as a killing mechanism. Hypercapnia best explains the selectivity of the extinction, but anoxia and euxinia probably contributed to the high mortality of the event. The persistence of anoxia through the Early Triassic may explain the slow recovery of marine life after the extinction. Models also show that anoxic events can cause catastrophic hydrogen sulfide emissions into the atmosphere (see below). The sequence of events leading to anoxic oceans may have been triggered by carbon dioxide emissions from the eruption of the Siberian Traps. In that scenario, warming from the enhanced greenhouse effect would reduce the solubility of oxygen in seawater, causing the concentration of oxygen to decline. Increased weathering of the continents due to warming and the acceleration of the

water cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly cons ...

would increase the riverine flux of

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

to the ocean. The phosphate would have supported greater primary productivity in the surface oceans. The increase in organic matter production would have caused more organic matter to sink into the deep ocean, where its respiration would further decrease oxygen concentrations. Once anoxia became established, it would have been sustained by a positive feedback loop because deep water anoxia tends to increase the recycling efficiency of phosphate, leading to even higher productivity. A severe anoxic event at the end of the Permian would have allowed sulfate-reducing bacteria to thrive, causing the production of large amounts of hydrogen sulfide in the anoxic ocean, turning it euxinic. Upwelling of this water may have released massive

emissions into the atmosphere and would poison terrestrial plants and animals and severely weaken the

ozone layer The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. It contains a high concentration of ozone (O3) in relation to other parts of the atmosphere, although still small in rel ...

, exposing much of the life that remained to fatal levels of UV radiation. Indeed,

biomarker In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, p ...

evidence for anaerobic photosynthesis by Chlorobiaceae (green sulfur bacteria) from the Late-Permian into the Early Triassic indicates that hydrogen sulfide did upwell into shallow waters because these bacteria are restricted to the photic zone and use sulfide as an electron donor. The hypothesis has the advantage of explaining the mass extinction of plants, which would have added to the methane levels and should otherwise have thrived in an atmosphere with a high level of carbon dioxide. Fossil spores from the end-Permian further support the theory: many show deformities that could have been caused by ultraviolet radiation, which would have been more intense after hydrogen sulfide emissions weakened the ozone layer.

Aridification

Analysis of the fossil river deposits of the floodplains indicate a shift from

meander A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank ( cut bank) and deposits sediments on an inner, convex ban ...

ing to braided river patterns, indicating a very abrupt drying of the climate. The climate change may have taken as little as 100,000 years, prompting the extinction of the unique '' Glossopteris'' flora and its associated herbivores, followed by the carnivorous

guild A guild ( ) is an association of artisans and merchants who oversee the practice of their craft/trade in a particular area. The earliest types of guild formed as organizations of tradesmen belonging to a professional association. They sometimes ...

. In the North China Basin, highly arid climatic conditions are recorded during the latest Permian, near the Permian-Triassic boundary, with a swing towards increased precipitation during the Early Triassic, the latter likely assisting biotic recovery following the mass extinction. Evidence from the Sydney Basin of eastern Australia, on the other hand, suggests that the expansion of semi-arid and arid climatic belts across Pangaea was not immediate but was instead a gradual, prolonged process. Apart from the disappearance of peatlands, there was little evidence of significant sedimentological changes in depositional style across the Permian-Triassic boundary. Instead, a modest shift to amplified seasonality and hotter summers is suggested by palaeoclimatological models based on weathering proxies from the region's Late Permian and Early Triassic deposits. In the Kuznetsk Basin of southwestern Siberia, an increase in aridity led to the demise of the humid-adapted cordaites forests in the region a few hundred thousand years before the Permian-Triassic boundary. This has been attributed to a broader poleward shift of drier, more arid climates during the late Changhsingian before the more abrupt main phase of the extinction at the Permian-Triassic boundary that disproportionately affected tropical and subtropical species.

Asteroid impact

A minority hypothesis holds that the impact event which formed the

Araguainha crater The Araguainha crater or Araguainha dome is an impact crater on the border of Mato Grosso and Goiás states, Brazil, between the villages of Araguainha and Ponte Branca. With a diameter of , it is the List of impact craters on Earth, largest known ...

, whose formation has been dated to , a possible temporal range overlapping with the end-Permian extinction, to have precipitated the mass extinction. The impact occurred around extensive deposits of oil shale in the shallow marine Paraná–Karoo Basin, whose perturbation by the seismicity resulting from impact likely discharged about 1.6 teratonnes of methane into Earth's atmosphere, buttressing the already rapid warming caused by hydrocarbon release due to the Siberian Traps. The large earthquakes generated by the impact would have additionally generated massive tsunamis across much of the globe. Despite this, most palaeontologists reject the impact as being a significant driver of the extinction, citing the relatively low energy (equivalent to 10⁵ to 10⁶ of TNT, around two orders of magnitude lower than the impact energy believed to be required to induce mass extinctions) released by the impact.

Supercontinent Pangaea

In the mid-Permian (during the Kungurian age of the Permian's Cisuralian epoch), Earth's major continental plates joined, forming a

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which lea ...

called

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 millio ...

, which was surrounded by the superocean, Panthalassa. Oceanic circulation and atmospheric weather patterns during the mid-Permian produced seasonal

monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal osci ...

s near the coasts and an arid climate in the vast continental interior. As the supercontinent formed, the ecologically diverse and productive coastal areas shrank. The shallow aquatic environments were eliminated and exposed formerly protected organisms of the rich continental shelves to increased environmental volatility. Pangaea's formation depleted marine life at near catastrophic rates. However, Pangaea's effect on land extinctions is thought to have been smaller. In fact, the advance of the therapsids and increase in their diversity is attributed to the late Permian, when Pangaea's global effect was thought to have peaked. While Pangaea's formation certainly initiated a long period of marine extinction, its impact on the "Great Dying" and the end of the Permian is uncertain.

Microbes

A hypothesis published in 2014 posits that a genus of

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic ad ...

ic archaea known as ''

Methanosarcina ''Methanosarcina'' is a genus of euryarchaeote archaea that produce methane. These single-celled organisms are known as anaerobic methanogens that produce methane using all three metabolic pathways for methanogenesis. They live in diverse e ...

'' was responsible for the event. Three lines of evidence suggest that these microbes acquired a new metabolic pathway via gene transfer at about that time, enabling them to efficiently metabolize acetate into methane. That would have led to their exponential reproduction, allowing them to rapidly consume vast deposits of organic carbon that had accumulated in the marine sediment. The result would have been a sharp buildup of methane and carbon dioxide in the Earth's oceans and atmosphere, in a manner that may be consistent with the ¹³C/¹²C isotopic record. Massive volcanism facilitated this process by releasing large amounts of

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...

, a scarce metal which is a cofactor for enzymes involved in producing methane. – Lay summary: On the other hand, in the canonical Meishan sections, the nickel concentration increases somewhat after the concentrations have begun to fall.

Combination of causes

Possible causes supported by strong evidence appear to describe a sequence of catastrophes, each worse than the last: the Siberian Traps eruptions were bad enough alone, but because they occurred near coal beds and the continental shelf, they also triggered very large releases of carbon dioxide and methane. The resultant global warming may have caused perhaps the most severe anoxic event in the oceans' history: according to this theory, the oceans became so anoxic, anaerobic sulfur-reducing organisms dominated the chemistry of the oceans and caused massive emissions of toxic hydrogen sulfide. However, there may be some weak links in this chain of events: the changes in the ¹³C/¹²C ratio expected to result from a massive release of methane do not match the patterns seen throughout the early Triassic; and the types of oceanic thermohaline circulation that may have existed at the end of the Permian are not likely to have supported deep-sea anoxia.

References

External links

* * * * * * * Podcast available. * * {{DEFAULTSORT:Permian-Triassic Extinction Event . . Events that forced the climate Extinction events Hypothetical impact events Meteorological hypotheses Permian events Permian life Triassic events Triassic life

Dating

Extinction patterns

Marine organisms

Terrestrial invertebrates

Terrestrial plants

Terrestrial vertebrates

Biotic recovery

Marine ecosystems

Terrestrial plants

Coal gap

Terrestrial vertebrates

Terrestrial invertebrates

Hypotheses about cause

Volcanism

Methane clathrate gasification

Hypercapnia and acidification

Anoxia and euxinia

Aridification

Asteroid impact

Supercontinent Pangaea

Microbes

Combination of causes

See also

References

Further reading

External links