Triassic–Jurassic extinction event
[42] Siliceous sponges dominated the immediate aftermath interval thanks to the enormous influx of silica into the oceans from the weathering of the CAMP's aerially extensive basalts.
[13] Olsen (1987) estimated that 42% of all terrestrial tetrapods became extinct at the end of the Triassic, based on his studies of faunal changes in the Newark Supergroup of eastern North America.
Although the earliest lissamphibians (modern amphibians like frogs and salamanders) did appear during the Triassic, they would become more common in the Jurassic while the temnospondyls diminished in diversity past the Triassic–Jurassic boundary.
Aetosaurs, kuehneosaurids, drepanosaurs, thecodontosaurids, "saltoposuchids" (like Terrestrisuchus), trilophosaurids, and various non-crocodylomorph pseudosuchians are all examples of Rhaetian reptiles which may have become extinct at the Triassic–Jurassic boundary.
[7] Herbivorous insects were minimally affected by the TJME; evidence from the Sichuan Basin shows they were overall able to quickly adapt to the floristic turnover by exploiting newly abundant plants.
[4] Overall, plants suffered minor diversity losses on a global scale as a result of the extinction, but species turnover rates were high and substantial changes occurred in terms of relative abundance and growth distribution among taxa.
[59] Evidence from Central Europe suggests that rather than a sharp, very rapid decline followed by an adaptive radiation, a more gradual turnover in both fossil plants and spores with several intermediate stages is observed over the course of the extinction event.
[61] Ferns and other species with dissected leaves displayed greater adaptability to atmosphere conditions of the extinction event,[62] and in some instances were able to proliferate across the boundary and into the Jurassic.
[61] In the Jiyuan Basin of North China, Classopolis content increased drastically in concordance with warming, drying, wildfire activity, enrichments in isotopically light carbon, and an overall reduction in floral diversity.
[63] In the Sichuan Basin, relatively cool mixed forests in the late Rhaetian were replaced by hot, arid fernlands during the Triassic–Jurassic transition, which in turn later gave way to a cheirolepid-dominated flora in the Hettangian and Sinemurian.
In the Newark Supergroup of the United States East Coast, about 60% of the diverse monosaccate and bisaccate pollen assemblages disappear at the Tr–J boundary, indicating a major extinction of plant genera.
[88][89][17] The isotopic composition of fossil soils and marine sediments near the boundary between the Late Triassic and Early Jurassic has been tied to a large negative δ13C excursion,[90][91][92] with values as low as -2.8%.
[93] Carbon isotopes of hydrocarbons (n-alkanes) derived from leaf wax and lignin, and total organic carbon from two sections of lake sediments interbedded with the CAMP in eastern North America have shown carbon isotope excursions similar to those found in the mostly marine St. Audrie's Bay section, Somerset, England; the correlation suggests that the TJME began at the same time in marine and terrestrial environments, slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, with both a critical CO2 greenhouse and a marine biocalcification crisis.
[94][95][96] The observed negative carbon isotope excursion is lower in some sites that correspond to what was then eastern Panthalassa because of the extreme aridity of western Pangaea limiting weathering and erosion there.
[19] Volcanic global warming has also been criticised as an explanation because some estimates have found that the amount of carbon dioxide emitted was only around 250 ppm, not enough to generate a mass extinction.
[110] The flood basalts of the CAMP released gigantic quantities of carbon dioxide,[111] a potent greenhouse gas causing intense global warming.
[115] In addition, the flood basalts intruded through sediments that were rich in organic matter and combusted it,[116][117][118] which led to the degassing of volatiles that further enhanced volcanic warming of the climate.
[128][129] Besides the carbon dioxide-driven long-term global warming, CAMP volcanism had shorter term cooling effects resulting from the emission of sulphur dioxide aerosols.
The authors propose that cold periods ("ice ages") induced by volcanic ejecta clouding the atmosphere might have favoured endothermic animals, with dinosaurs, pterosaurs, and mammals being more capable at enduring these conditions than large pseudosuchians due to insulation.
[156] In northeastern Panthalassa, episodes of anoxia and euxinia were already occurring during the Rhaetian before the TJME, making its marine ecosystems unstable even before the main crisis began.
[164] The persistence of anoxia into the Hettangian age may have helped delay the recovery of marine life in the extinction's aftermath,[150][165] and recurrent hydrogen sulphide poisoning likely had the same retarding effect on biotic rediversification.
[167][168] A spike in the abundance of unseparated tetrads of Kraeuselisporites reissingerii has been interpreted as evidence of increased ultraviolet radiation flux resulting from ozone layer damage caused by volcanic aerosols.
Within his 1958 study recognizing biological turnover between the Triassic and Jurassic, Edwin H. Colbert's proposal was that this extinction was a result of geological processes decreasing the diversity of land biomes.
He considered the Triassic period to be an era of the world experiencing a variety of environments, from towering highlands to arid deserts to tropical marshes.
[171] The site of Hochalm in Austria preserves evidence of carbon cycle perturbations during the Rhaetian preceding the Triassic-Jurassic boundary, potentially having a role in the ecological crisis.
However, there is still some evidence that marine life was affected by secondary processes related to falling sea levels, such as decreased oxygenation (caused by sluggish circulation), or increased acidification.
Olsen et al. (1987) were the first scientists to link the Manicouagan crater to the Triassic–Jurassic extinction, citing its age which at the time was roughly considered to be Late Triassic.
[178] Onoue et al. (2016) alternatively proposed that the Manicouagan impact was responsible for a marine extinction in the middle of the Norian which affected radiolarians, sponges, conodonts, and Triassic ammonoids.
[189] Various trace metal ratios, including palladium/iridium, platinum/iridium, and platinum/rhodium, in rocks deposited during the TJME have numerical values very different from what would be expected in an extraterrestrial impact scenario, providing further evidence against this hypothesis.
[9] The current rate of carbon dioxide emissions is around 50 gigatonnes per year, hundreds of times faster than during the latest Triassic, although the lack of extremely detailed stratigraphic resolution and pulsed nature of CAMP volcanism means that individual pulses of greenhouse gas emissions likely occurred on comparable timescales to human release of warming gases since the Industrial Revolution.
