Permian–Triassic extinction event

[54][55] The negative carbon isotope excursion's magnitude was 4-7% and lasted for approximately 500 kyr,[56] though estimating its exact value is challenging due to diagenetic alteration of many sedimentary facies spanning the boundary.

The groups with the highest survival rates generally had active control of circulation, elaborate gas exchange mechanisms, and light calcification; more heavily calcified organisms with simpler breathing apparatuses suffered the greatest loss of species diversity.

[125] The Lilliput effect, the phenomenon of dwarfing of species during and immediately following a mass extinction event, has been observed across the Permian-Triassic boundary,[126][127] notably occurring in foraminifera,[128][129][130] brachiopods,[131][132][133] bivalves,[134][135][136] and ostracods.

At the same time that marine invertebrate macrofauna declined, these large woodlands died out and were followed by a rise in diversity of smaller herbaceous plants including Lycopodiophyta, both Selaginellales and Isoetales.

[184] Typical taxa of shelly benthic faunas were now bivalves, snails, sea urchins and Malacostraca, whereas bony fishes[185] and marine reptiles[186] diversified in the pelagic zone.

[193] Marine post-extinction faunas were mostly species-poor and were dominated by few disaster taxa such as the bivalves Claraia, Unionites, Eumorphotis, and Promyalina,[194] the conodonts Clarkina and Hindeodus,[195] the inarticulate brachiopod Lingularia,[194] and the foraminifera Earlandia and Rectocornuspira kalhori,[196] the latter of which is sometimes classified under the genus Ammodiscus.

[208] Regional differences in the pace of biotic recovery existed,[209][210] which suggests that the impact of the extinction may have been felt less severely in some areas than others, with differential environmental stress and instability being the source of the variance.

[11][225][226] Continual episodes of extremely hot climatic conditions during the Early Triassic have been held responsible for the delayed recovery of oceanic life,[227][228] in particular skeletonised taxa that are most vulnerable to high carbon dioxide concentrations.

[251] Major brachiopod rediversification only began in the late Spathian and Anisian in conjunction with the decline of widespread anoxia and extreme heat and the expansion of more habitable climatic zones.

[286] Ichnological evidence suggests that recovery and recolonisation of marine environments may have taken place by way of outward dispersal from refugia that suffered relatively mild perturbations and whose local biotas were less strongly affected by the mass extinction compared to the rest of the world's oceans.

However, in the late Dienerian, a major shift towards assemblages dominated by cavate trilete spores took place, heralding widespread deforestation and a rapid change to hotter, more humid conditions.

[309] Lystrosaurus, a pig-sized herbivorous dicynodont therapsid, constituted as much as 90% of some earliest Triassic land vertebrate fauna, although some recent evidence has called into question its status as a post-PTME disaster taxon.

[50][340][341][19][342] A study of the Norilsk and Maymecha-Kotuy regions of the northern Siberian platform indicates that volcanic activity occurred during a few enormous pulses of magma, as opposed to more regular flows.

[356][9] Evidence also points to volcanic combustion of underground fossil fuel deposits, based on paired coronene-mercury spikes[357][31] coinciding with geographically widespread mercury anomalies and the rise in isotopically light carbon.

[349] The change of the eruptions from flood basalt to sill dominated emplacement, liberating even more trapped hydrocarbon deposits, coincides with the main onset of the extinction[28] and is linked to a major negative δ13C excursion.

"[374][375] 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.

Carbon isotope fluctuations suggest that massive Siberian Traps activity recurred many times during the Early Triassic,[394][395] a finding corroborated by mercury spikes,[396] causing further extinction events during the epoch.

[413] The configuration of the world's landmasses into one supercontinent would also mean that the global gas hydrate reservoir was lower than today, further damaging the case for methane clathrate dissolution as a major cause of the carbon cycle disruption.

In marine organisms, relatively modest but sustained increases in CO2 concentrations hamper the synthesis of proteins, reduce fertilization rates, and produce deformities in calcareous hard parts.

[462] Along the Panthalassan coast of South China, oxygen decline was also driven by large-scale upwelling of deep water enriched in various nutrients, causing this region of the ocean to be hit by especially severe anoxia.

[476] Some scientists have challenged the anoxia hypothesis on the grounds that long-lasting anoxic conditions could not have been supported if Late Permian thermohaline ocean circulation conformed to the "thermal mode" characterised by cooling at high latitudes.

[484] 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.

[485] 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.

[486] 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.

Drying of this basin 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.

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.

[513] Yet, subduction should not be entirely accepted as an explanation for the lack of evidence: as with the K-T event, an ejecta blanket stratum rich in siderophilic elements (such as iridium) would be expected in formations from the time.

[36] A 2017 paper noted the discovery of a circular gravity anomaly near the Falkland Islands which might correspond to an impact crater with a diameter of 250 km (160 mi),[521] as supported by seismic and magnetic evidence.

[523] John Gribbin argues that the Solar System last passed through a spiral arm of the Milky Way around 250 million years ago and that the resultant dusty gas clouds may have caused a dimming of the Sun, which combined with the effect of Pangaea to produce an ice age.

[524] The PTME has been compared to the current anthropogenic global warming situation and Holocene extinction due to sharing the common characteristic of rapid rates of carbon dioxide release.