The Permian-Triassic ( P-Tr or PT ) extinction events , colloquially known as Great Dead , End Permian Extinction , or Great Permian Extinction , occurs around 252 Ma (million years ago), forming a boundary between Permian and Triassic geology periods , as well as the Paleozoic and Mesozoic era. This is the most severe extinction event known on Earth, with up to 96% of all marine species and 70% of extraterrestrial vertebrate species. This is the only known mass extinction of insects. About 57% of all biological families and 83% of all genera are extinct. Because so much biodiversity is lost, the recovery of life on Earth is significantly longer than after any other extinction event, perhaps up to 10 million years. Studies in Bear Lake County near Paris, Idaho show a rapid and dynamic rebound in the marine ecosystem, which represents a remarkable survival.
There is evidence for one or three different pulses, or phases, of extinction. The suggested mechanisms for the latter include one or more major meteor impact events, large volcanism such as Siberia Traps, and coal or gas fires or fires occurring, and greenhouse effects triggered by the sudden release of methane from the ocean floor due to methane clathrate dissociation according to the klathrate gun hypothesis or methane-producing microbes known as methanogens. Possible contributions to gradual change include sea-level changes, anoxia increases, increased aridity, and climate change-driven ocean shifts.
Video Permian-Triassic extinction event
Dating with extinction Edit
Until 2000, it was thought that rock sequences covering the Permian-Triassic boundary were too few and contained too many gaps for scientists to pinpoint the details. However, it is now possible to date extinctions with millennium precision. Zircon U-Pb comes from five volcanic ash beds from the Global Stratotype Section and Point for the Permian-Triassic border in Meishan, China, setting a high resolution age model for extinction - allowing exploration of the relationship between global environmental disorders, carbon cycle disturbances, mass extinctions, and recovery on the millennium time scale. Extinction occurs between 251.941 Â ± 0.037 and 251.880 Â ± 0.031 Ma, duration 60 Ã, Â ± 48 ka. A large global decline (about 0.9%), abruptly in stable isotope ratios <13 /soup>
C with the 12
C , coinciding with this extinction, and sometimes used to identify Permian-Triassic boundaries in rocks unsuitable for radiometric dating. Further evidence for environmental changes around the P-Tr boundary shows an increase of 8Ã, Â ° C (14Ã, Â ° F) temperatures, and an increase of CO
2 level by 2000Ã, ppm (for comparison, the concentration immediately before the industrial revolution is < span> 280Ã, ppm , and the current number is about 410 ppm). There is also evidence of increased ultraviolet radiation reaching Earth, causing mutation of plant spores.
It has been argued that the Permian-Triassic boundary is associated with a sharp increase in the abundance of sea and terrestrial fungi, caused by the sharp increase in the number of dead plants and animals fed by fungi. In the meantime "mushroom spike" is used by some paleontologists to identify Permian-Triassic boundaries in rocks unsuited to radiometric dating or fossil index deficiencies accordingly, but even advocates of the fungal spike hypothesis suggest that "mushroom spike" may be a recurring phenomenon created by the earliest ecosystem of post-extinction in Triass. The idea of ​​mushroom spikes has been criticized for several reasons, including: Reduviasporonite , the most commonly suspected fungal spores, actually algae fossils; that spike did not appear all over the world; and in many places it does not fall on the Permian-Triassic boundary. The algae, mistakenly identified as mushroom spores, can even represent a transition to the Triassic dominated world of lakes and not the earliest Triassic death zone and decompose in several layers of terrestrial fossils. More recent chemical evidence agrees better with fungal origin for Reduviasporonites , diluting this criticism.
Uncertainty exists regarding the duration of extinction as a whole and about the time and duration of extinction of various groups in the larger process. Some evidence suggests that there were some pulse extinctions or that extinctions spread for several million years, with a sharp peak in the last million years of the Permian. The statistical analysis of some very high fossil layers in Meishan, Zhejiang Province in southeast China, shows that the major extinctions swarm around one peak. Recent research shows that different groups become extinct at different times; for example, while difficult to date really, the extinction of ostracod and brachiopod is separated by 670-117000 years. In well-preserved order in eastern Greenland, the decline of animals is concentrated in periods of 10 to 60Ã, thousands of years long, with plants taking an additional several hundred thousand years to show the full impact of the event.. An older theory, still supported in recent papers, is that there are two major extinctions of 9.4 million years apart pulses, separated by periods of extinction far above the background level, and that the final extinction kills only about 80% marine species live at the time while other losses occur during the first pulse or the interval between pulses. According to this theory, one of these extinctions occurred at the end of the Guadalupian era of the Permian. For example, all but one of the living genera dinocephalia die at the end of Guadalupian, as well as Verbeekinidae, a large fussal foraminifera family. The impact of the final extinction-Guadalupian on marine organisms appears to vary between locations and between taxonomic groups - brakiopods and corals have severe losses.
Maps Permian-Triassic extinction event
The blackout pattern Edit
Marine organism Edit
Marine invertebrates suffered the greatest losses during the P-Tr extinction. This evidence is found in samples from the southern Chinese section of the P-Tr boundary. Here, 286 of 329 marine invertebrate genes disappear in the last two sedimentary zones containing the con- dons of the Permian. Decrease in diversity may be due to a sharp increase in extinction, not a decrease in speciation.
Extinction primarily affects organisms with calcium carbonate frameworks, especially those that depend on stable levels of CO 2 to produce their skeletons. The organism is susceptible to ocean acidification effects resulting from an increase in atmospheric CO 2 .
Among the benthic organisms, extinction events multiplied the rate of extinction of the background, and therefore led to the loss of maximum species for taxa that had a high background of extinction (with implications, taxa with high rotation). The rate of extinction of marine organisms is a disaster.
Surviving marine invertebrate groups include: articulate brutes (those with hinges), which have experienced a slow decline in numbers since the extinction of P-Tr; The Order of Ceratitides from Ammon; and crinoids ("sea lilies"), which are almost extinct but then become abundant and diverse.
The group with the highest survival rate generally have active circulation control, complex gas exchange mechanism, and mild calcification; more calcified organisms with simpler breathing apparatus suffer the greatest loss of species. In the case of brakiopods, at least, the surviving taxa are generally small, rare members of previously diverse communities.
Ammonoids, which have suffered a long-term decline for 30 million years since the Roadian (the Permian center), experienced a selective extinction 10 million years before the main event, at the end of the Capitanian stage. In this early extinction, which greatly reduced the disparities, or different ecological unions, environmental factors were found to be responsible. Diversity and disparity are increasingly far to the limit of P-Tr; The extinction here (P-Tr) is not selective, consistent with the catastrophic initiator. During Triass, diversity increased rapidly, but disparities remained low.
The range of morphospace occupied by ammonoids, ie, possible shapes, shapes, or structures, becomes more limited when the Permian develops. Several million years into the Triassic, the original range of the ammonoid structure is once again inhabited, but the parameters are now divided differently among the clades.
Invertebrates on land Edit
Permian has a great diversity in insect species and other invertebrates, including the largest insects ever. The final permian is the only known mass extinction of insects, with eight or nine order of insects becoming extinct and ten more diminished in diversity. Palaeodictyopteroids (insects with piercings and mouth sucking) begin to decline during the middle of the Permian; This extinction has been linked to changes in flora. The greatest decrease occurs in the Final Permian and may not be directly caused by weather-related flower transitions.
Most groups of fossil insects found after the Permian-Triassic boundary differ significantly from the previous one. Of the Paleozoic insect groups, only Glosselytrodea, Miomoptera, and Protorthoptera have been found in sediment after extinction. Caloneurodean, monuran, paleodictyopteroids, protelytropterans, and protodonat extinct at the end of Permian. In well-documented Triassic sediments, the fossil is very much composed of modern fossilized insect groups.
Terrestrial plants Edit
Crop ecosystem responses Edit
The geological recordings of terrestrial plants are rare and largely based on pollen and spore research. Plants are relatively immune to mass extinctions, with the impact of all massive "massive" mass extinctions at the family level. Even the observed reductions in species diversity (50%) may be largely due to taphonomic processes. However, massive ecosystem rearrangements do occur, with abundance and distribution of crops changing profoundly and all forests virtually disappearing; The Palaeozoic flora barely survives from this extinction.
At the P-Tr limit, the dominant interest groups change, with many groups of terrestrial plants entering a sudden decline, such as Cordaites (gymnospermae) and Glossopteris (fern seeds). The dominant Gymnosperm genus is replaced post-border by lycophytes - lycophytes still present are recolonizers of disturbed areas.
Palitnologi or pollen studies from East Greenland from layers of sedimentary rocks specified during the period of extinction show a dense parknosperm forest park before the event. At the same time the marine invertebrate macrofauna decreases, this large forest dies and is followed by an increase in the diversity of smaller herbaceous plants including Lycopodiophyta, both Selaginellales and Isoetales . Later, another gymnosperma group became dominant again but again suffered a great death. This cycle shift occurs several times during the period of extinction and thereafter. This fluctuation of the dominant flora between woody and herb taxa indicates chronic environmental pressures resulting in the loss of most forest plant species. Succession and extinction of the plant community does not coincide with the shift in the value of ? 13 C, but it happens many years later. The restoration of the gymnosperm forest takes 4-5 million years.
Coal restriction Edit
No known coal deposits from the Early Trias, and those in Middle Trias are thin and of poor quality. This "coal gap" has been described in many ways. It has been suggested that new, more aggressive fungi, insects and vertebrates evolved, and killed large numbers of trees. The decomposer itself suffered great loss of species during the extinction, and was not considered a possible cause of the coal gap. It could be just that all the plants that make up the coal have become extinct by P-Tr extinction, and take 10 million years to set new plants to adapt to the humid and acid conditions of the peat swamp. Abiotic factors (factors not caused by organisms), such as decreased rainfall or increased clastic sediment input, may also be to blame.
On the other hand, the lack of coal may only reflect the scarcity of all known sediments from the Early Triassic. The coal-producing ecosystem, instead of disappearing, may have moved to an area where we do not have a sedimentary record for the Early Triassic. For example, in eastern Australia, cold climates have been the norm for long periods of time, with peat swamp ecosystems tailored to this condition. About 95% of these peat-producing plants local are extinct on the P-Tr boundary; Interestingly, coal deposits in Australia and Antarctica disappeared significantly before P-Tr boundaries.
Inland vertebrates Edit
There is enough evidence to show that more than two-thirds of the terrestrial labyrinthodont amphibians, sauropsid ("reptile") and therapsid families ("proto-mammals") are extinct. Large herbivores suffer the heaviest loss.
All of the ansexide Permia reptiles die unless prokolofonoid (although testudin has anapsid skull morphologically , now considered to have evolved separately from the diapidated ancestor). Pelycosaurs died before the end of Permian. Too few fossils of merged Permian have been found to support any conclusions about the Permian extinction effect on diapsids (the "reptile" group from which lizards, snakes, crocodiles, and dinosaurs (including birds) evolved).
The surviving groups suffered the loss of a very large species, and some groups of land vertebrates were nearly extinct in the Permian end. Some surviving groups did not survive this period long, while others who barely survived continued to produce a diverse and durable lineage. But it took millions of years for terrestrial vertebrate fauna to recover fully both numerically and ecologically.
Possible explanation of these patterns Edit
Analysis of marine fossils from end-stage Changhsingian Permian found that low-tolerance marine organisms for hypercapnia (high concentrations of carbon dioxide) had high extinction rates, while the most tolerant organisms had fewer disadvantages.
The most vulnerable marine organisms are organisms that produce hard calcareous parts (ie, from calcium carbonate) and have low metabolic rates and weak respiratory systems - especially calcareous sponges, rugosa corals and tabulates, calcite-deposit brakiopods, bryozoans, and echinodermata; about 81% of the genera became extinct. Close relatives without a hard part of sweating suffered only minor losses, such as sea anemones, from which modern coral evolved. Animals with high metabolic rates, the respiratory system is well developed, and the non-calcareous hard part has negligible disadvantages - except for conodons, where 33% of the genera die.
This pattern is consistent with what is known about the effects of hypoxia, the lack but not the total absence of oxygen. However, hypoxia is not the only mechanism of killing of marine organisms. Almost all continental shelf waters will become highly hypoxic to account for extinction, but such a disaster will make it difficult to explain highly selective extinction patterns. The Late Permian and Early Trias atmosphere models showed significant but prolonged decreases in atmospheric oxygen levels, without acceleration near the P-Tr boundary. Minimum atmospheric oxygen levels in the Early Trias are never less than today's levels - the decrease in oxygen levels does not match the temporal pattern of extinction.
Marine organisms are more sensitive to changes in CO 2 (carbon dioxide) levels than terrestrial organisms for various reasons. CO 2 28 times more soluble in water than oxygen. Marine animals typically function with lower CO concentrations 2 in their bodies than inland animals, as removal of CO 2 in air-breathing animals is hampered by the need for gas to pass through respiratory system membranes (alveolus of the lung, trachea, and the like), even when CO 2 diffuses more easily than oxygen. In marine organisms, a relatively small but continuous increase in the concentration of CO 2 inhibits protein synthesis, reduces fertilization rates, and produces deformities in chalky hard parts. In addition, an increase in CO 2 concentration is unavoidable in relation to ocean acidification, consistent with the preferential extinction of heavy calcification taxa and other signals in rock records indicating more acidic seas. The decrease in ocean pH was calculated to 0.7 units.
It is difficult to analyze the extinction and survival rates of soil organisms in detail, as some layers of terrestrial fossils extend beyond the Permian-Triassic border. The insect experiments are very different from those in the Permian, but the gaps in the fossil record of insects extend approximately 15 million years from the late Permian to the early Triassic. The most notable record of vertebrate changes on the Permian-Triassic border occurred at Karoo Supergroup South Africa, but statistical analysis so far has not yielded a clear conclusion. However, the analysis of river fossil deposits from floodplains indicates a shift from a river pattern winding to the fabric, suggesting a sudden climatic drainage. Climate change may have taken only 100,000 years, driving the unique extinction of the glossopteris flora and its herbivores, followed by a carnivorous guild. The Permian end extinction does not occur on the instantaneous time horizon; in particular, the extinction of interest is delayed in time.
Biotic Recovery Edit
Previous analyzes have shown that life on Earth is recovering rapidly after the Permian extinction, but this is largely in the form of a catastrophic taxa, opportunistic organisms such as hardy
A study published in the journal Science found that during Great Extinction, ocean surface temperatures reached 40 Ã, Â ° C (104Ã, Â ° F) in some places. This explains why the recovery is so long: too hot to survive. Anoxic water may also delay recovery.
During the early Triassic (4 to 6 million years after the extinction of P-Tr), plant biomass was insufficient to form coal deposits, implying a limited mass of food for herbivores. The river pattern in Karoo turns from winding into fabric, indicating that vegetation there is very rare for a long time.
Each major segment of the early Triassic ecosystem - plants and animals, sea and land - is dominated by a small number of genera, which appear almost all over the world, for example: the herbivorous therapid Lystrosaurus (which accounts for about 90% of land vertebrates Early Triassic) and bivalvia Claraia , Eumorphotis , Unionites and Promylina . Healthy ecosystems have a larger number of genera, each living in some preferred habitat type.
Disaster taxa takes advantage of the devastated ecosystem and enjoys a temporary population explosion and increase in their region. Microconchids are the dominant component of the early Triassic encrust collection of the poor. For example: Lingula (a brachiopod); stromatolites, which have been limited to the marginal environment since Ordovisium; pleuromeia (small thin plants); Dicroidium (fern seed).
Sea ecosystem changes Edit
Before the extinction, about two-thirds of marine animals sessile and cling to the seabed. During the Mesozoic, only about half of the sea animals are sessile while the rest live freely. Analysis of marine fossils from the period showed a decrease in abundance of sessile epifonia suspension feeders such as brakiopods and sea lilies and the increasing of more complex cellular species such as snails, sea urchins and crabs.
Prior to the mass extinction of the Permia, complex and simple marine ecosystems were equally common; after the recovery of mass extinctions, complex communities outnumbered simple communities by almost three to one, and an increase in predatory pressure led to the Mesozoic Marine Revolution.
Bivalves are quite rare before the extinction of P-Tr but became numerous and varied in the Triassic, and one group, the rudir shells, became the main Mesozoic reef builder. Some researchers think many of these changes occur within 5 million years between two major extinction waves.
Crinoids ("sea lilies") suffer selective extinction, resulting in decreases in various forms. Their subsequent adaptive radiation is fast, and results in forms that have flexible arms wide; motility, especially the response to predation pressure, is also becoming much more common.
Inland vertebrates Edit
Lystrosaurus , the pig's dicynodont herbivir therapid, comprises as much as 90% of some early vertebrate ground tassage fauna. Theraphoid cynodont smaller carnivores also survive, including the ancestors of mammals. In the southern African Karoo region, therocephalian Tetracynodon , Moschorhinus and Ictidosuchoides survived, but did not seem to be abundant in Triass.
Archosaurs (which include dinosaur and crocodile ancestors) were initially more rare than therapsids, but they began replacing therapsids in the mid-Triassic. In the mid to late Triassic, dinosaurs evolved from a group of archosaurs, and continued to dominate terrestrial ecosystems during Jurassic and Cretaceous. This "Trial Taking" may have contributed to the evolution of mammals by forcing surviving therapsids and substituting their mammals to live as small, especially nocturnal insectivores; nocturnal life may force at least mammals to develop feathers and higher metabolic rates, while losing part of the color-sensitive receptors of color-sensitive reptiles and birds are preserved.
Some temnospondyl amphibians experience relatively rapid recovery, although they are almost extinct. Mastodonsaurus and trematosauria are major aquatic and semiaquatic predators during most of the Triassic, some prey on tetrapods and others on fish.
Land vertebrates took a very long time to recover from the extinction of P-Tr; Paleontologist Michael Benton estimates that recovery is incomplete until 30 million years after fainting, ie not until the Final Triassic, where dinosaurs, pterosaurs, crocodiles, archosaurs, amphibians, and mammals have many and varied.
Cause Edit
The precise determination of the cause or cause of the Permian-Triassic extinction event is difficult, largely because of the catastrophe occurred more than 250 million years ago, and since then much evidence will show the cause has been destroyed or hidden deep within the Earth under many layers of rock. The seafloor is also completely recycled every 200 million years by plate tectonic processes and seafloor deployment, leaving no useful indication under the oceans.
Scientists have collected enough evidence of the cause, and several mechanisms have been proposed for extinction events. The proposal includes both disastrous and gradual processes (similar to those theorized for the Cretaceous-Paleogene extinction event).
- The catastrophic group includes one or more major collision events, increased volcanism and sudden release of methane from the seafloor, either due to the separation of methane hydrate deposits or organic metabolism of carbon deposits by microbes methanogenic.
- Group stages including sea level changes, anoxia boost, and increased agility.
Any hypothesis about the cause must explain the selectivity of the event, which affects the organism with the most severe calcium carbonate framework; long periods (4 to 6 million years) before recovery begins, and minimal levels of biological mineralization (though inorganic carbon deposited) after recovery begins.
Impact events Edit
Evidence that impact events may have caused the Cretaceous-Paleogene (Cretaceous-Tertiary) extinction event has led to speculation that similar impacts may have been the cause of other extinction events, including the extinction of P-Tr, and thus to seek evidence of impact on other extinction and craters have a big impact on the right age.
The reported evidence for the impact events of the P-Tr-bound rate includes the shaken quartz of quartz in Australia and Antarctica; fullerenes trap noble gases outside the earth; meteorite shards in Antarctica; and grains rich in iron, nickel and silicon, which may be created by an impact. However, the accuracy of most of these claims has been challenged. For example, quartz from Graphite Peak in Antarctica, once considered "shocked", has been reexamined by an optical electron microscope and transmission. The observed feature is not summed up by surprise, but rather for plastic deformation, consistent with formation in tectonic environments such as volcanism.
The collision crater on the seafloor will be evidence of the possible cause of the extinction of P-Tr, but such craters have now disappeared. Since 70% of the Earth's current surface is the ocean, asteroid or comet fragments may now be twice as likely to hit the ocean as it would hit the land. However, the Earth's oldest sea floor crust is 200 million years old because it continues to be destroyed and renewed with spread and subduction. Thus, the craters produced by enormous impacts can be covered by widespread flooding from below after the crust leaks or weakens. However, subduction should not be entirely accepted as an explanation for why no strong evidence can be found: as in KT events, a siderophilic-rich blanket blanket blanket (such as iridium) is expected to be seen in the formation of time..
Major impacts may have triggered other extinction mechanisms described below, such as the Siberian Traps eruption at one of the impact sites or antipodes of the impact site. The sudden impact also explains why more species do not evolve quickly to survive, as expected if the Permian-Triassic event is slower and less global than meteorite impacts.
Possible impacted sites Edit
Several possible crater impacts have been proposed as impact sites causing P-Trun extinctions, including the structure of Bedout 250 km (160 mi) off the northwest coast of Australia and the hypothesized Wilkes Land crater of 480 km (300 mi) of Antarctic East. In any case, the idea that the impact is responsible has not been proven and has been heavily criticized. In the case of Wilkes Land, the age of the sub-ice geophysical feature is highly uncertain - perhaps slower than the Permian-Triassic extinction.
The 40 km (km) Araguainha Crater in Brazil was recently dated 254.7 ± 2.5 million years ago, overlapping with an estimated Permo-Triassic boundary. Most of the local stone is oil shale. Estimates of energy released by Araguainha's impact are not enough to be a direct cause of global mass extinctions, but tremors of huge local earth will release large amounts of oil and gas from crushed stone. Sudden global warming could trigger a Permian-Triassic extinction.
In May 1992, Michael R. Rampino published an abstract for the American Geophysical Union which noted the discovery of a circular gravity anomaly near the Falkland Islands. He suggested this structure might suit the impact crater with a diameter of 250 km (160 mi). In August 2017, Rampino, Maximilliano Rocca and Jaime Baez Presser followed up with papers that provide further seismic and magnetic evidence that the structure is a collision crater. Estimated age of structures ranges up to 250 million years. If, in fact, this is a collision crater, it will be much larger than the famous Chicxulub crater with a depth of 180 km (km) associated with further extinction events.
Volcanism Edit
Permian's final stage has two basal flood events. The small, Emeishan Traps in China, occurred at the same time as the end of the extinction of Guadalupian, in the area close to the equator at the time. The basal eruption flood that produces the Siberian Trap is one of the largest known volcanic events on Earth and encompasses over 2,000,000 square kilometers (770,000 sq.l. mi) with lava. The date of the Siberian Traps eruption and the extinction event are in good agreement.
Emeishan and Siberian Traps eruptions may have caused dust clouds and acidic aerosols, which would block sunlight and interfere with photosynthesis both on land and in oceanic photon zones, causing the food chain to collapse. The eruption may also cause acid rain when the aerosol is swept out of the atmosphere. It may have killed ground plants and mollusks and planktonic organisms that have calcium carbonate shells. The eruption will also emit carbon dioxide, causing global warming. When all the clouds of dust and aerosols drift away from the atmosphere, excess carbon dioxide will still exist and the warming will take place without the mitigating effect.
The Siberian traps have unusual features that make them even more dangerous. Pure flood basalt produces fluid, low viscosity lava and does not throw debris into the atmosphere. It seems, however, that 20% of the output of the Siberian Trap eruption is pyroclastic (composed of ash and other debris thrown high into the atmosphere), enhancing the short-term cooling effect. Basalt lava erupts or penetrates carbonate rocks and becomes sediments that are in the process of forming large coal seams, both of which will emit large amounts of carbon dioxide, leading to a stronger global warming once dust and aerosols settle.
In January 2011, a team, led by Stephen Grasby of the Canadian-Canada Geological Survey, reported evidence that volcanism causes a massive layer of coal to ignite, possibly releasing more than 3 trillion tons of carbon. The team found the deposition of ash in layers of rock in close proximity to what is now called Lake Buchanan. According to their article, "coal ash dispersed by an explosive Siberian Trap eruption would be expected to have the release of associated toxic elements in affected bodies where the flying ash mud develops.... The megascale mafic eruption is a long-lived event that will allow buildup significant global ash cloud. "In a statement, Grasby said," In addition to this volcano that causes fires through coal, the ashes are vomited highly toxic and released in soil and water, potentially contributing to the worst extinction events in Earth's history. " In 2013, a team led by QY Yang reported the total volatile sums emitted from the Siberian Traps were 8.5 ÃÆ'â € "10 7 Tg CO 2 , 4.4 ÃÆ'â 6 Tg CO, 7.0 ÃÆ'â € "10 6 Tg H 2 S and 6.8 ÃÆ'â €" 10
By 2015, evidence and timelines suggest the extinction was caused by events in the Great Frozen province of the Siberian Trap.
Methane hydrate gasification Edit
Scientists have found evidence worldwide about a rapid decline of about 1% in the isotope ratios in carbonate rocks from the late Permian. This is the first, largest, and fastest of a series of negative and positive visits (decrease and increase in the ratio of 13 C/ 12 C) that continues until the isotope ratios are suddenly stabilized in the middle Trias, soon after it was followed by the restoration of the life forms of calcifying (an organism that uses calcium carbonate to build hard parts like shellfish).
Various factors may have contributed to a decrease in the ratio of 13 C/ 12 C, but most were not enough to account for the full amount observed:
- The gas from volcanic eruption has a 13 ratio of C/ 12 C about 0.5 to 0.8% below standard (? 13 C about -0.5 to -0.8%), but the assessment made in 1995 concluded that the amount needed to produce a reduction of about 1.0% worldwide requires an eruption which is larger by order of magnitude than to which evidence has been found. (However, this analysis is only directed to CO 2 produced by magma itself, not from interactions with carbon-bearing sediment, as proposed at a later date.)
- The decrease in organic activity will extract 12 C slower than the environment and leave much more to put in the sediment, thus reducing the soup 13 C/<> 12 C ratio. Preferred biochemical processes use lighter isotopes because chemical reactions are essentially driven by electromagnetic forces between atoms and lighter isotopes respond more quickly to this force, but studies of a smaller decrease of 0.3 to 0.4% in 13 C/ 12 C (? 13 C -3 ke -4Ã,?) On Thermal Termal Paleocene-Eocene (PETM ) concluded that even transferring all the organic carbon (in organisms, soils, and dissolved in the oceans) into sediment would not be enough: even such large burial material in 12 C would not result in a smaller decrease 'in 13 C/ 12 C the ratio of rocks around the PETM.
- The buried organic sediments have a 13 ratio of C/ 12 C 2.0 to 2.5% below normal (? < soup> 13 C -2.0 to -2.5%). Theoretically, if sea levels drop sharply, shallow sea sediments will be exposed to oxidation. But 6500-8400 gigatonnes (1 gigaton = 10 9 metric ton) organic carbon must be oxidized and returned to the ocean-atmosphere system in less than a few hundred thousand years to reduce 13 C/ 12 C ratio of 1.0%, which is not considered a realistic possibility. In addition, sea levels are rising rather than falling at the moment of extinction.
- Instead of a sudden drop in the sea surface, intermittent intermittent periods of hypoxoxia and subsea anoxia (high and low oxygen or zero-oxygen oxygen conditions) may have caused soup 13 C/<> 12 C fluctuation ratio in Initial Triage; and global anoxia may be responsible for end-Permian blips. The late Permians and early Triassic continents are more clustered in the tropics than they are today, and large tropical rivers will dump the sediment into smaller, partially closed ocean basins at low latitudes. Such conditions support oxic and anoxic episodes; the oxyc/anoxic condition will produce rapid release, of large amounts of organic carbon, which has a low C < 13 C/ 12 C ratio because the biochemical process uses lighter isotopes. That or any other organic based reason may have been responsible for that and the old Proterozoic/Cambrian pattern ratio fluctuates 13 C/ 12 C.
Other hypotheses include massive mass poisoning that releases substantial CO 2 and reorganizes the long-term global carbon cycle.
Before considering inclusion of grain-carbonate sediment by volcanism, the proposed mechanism is only sufficient to cause a 1% global reduction in the 13 ratio C/ 12 C is release. methane from methane clathrates. The carbon cycle model confirms that it will have enough effect to produce observed reductions. Clathrates of methane, also known as methane hydrates, consist of methane molecules trapped in water molecules. Methane, produced by methanogens, has a 13 C/ 12 C ratio of about 6.0% below normal (? 13 C -6.0%). In the right combination of pressure and temperature, he is trapped in a clathrat close enough to the surface of permafrost and in much greater quantities on the continental fringe (deeper continental shelf and deeper seabed near them). Oceanic methane hydrids are usually found buried in sediments where seawater is at least 300 m (980Ã, ft) deep. They can be found up to about 2,000 m (6,600 ft) below the sea floor, but usually only about 1,100 m (3,600 ft) below the ocean floor.
The area covered by lava from the Siberian Traps eruption is approximately twice larger than originally estimated, and most of the additional areas are shallow seas at that time. The seafloor may contain hydrate hydrate deposits, and lava causes the precipitate to dissociate, releasing large quantities of methane. The large release of methane can cause significant global warming because methane is a very powerful greenhouse gas. Strong evidence suggests that global temperatures rise by about 6 ° C (10.8 ° F) near the equator and therefore more at higher latitudes: a sharp decrease in the oxygen isotope ratio ( 18 O/ 16 O); the extinction of the Glossopteris ( Glossopteris and the growing plants in the same area), which require a cold climate, with replacement by the typical flora of low paleolatitudes.
However, the pattern of isotopic shifts expected to result from massive methane release does not match the pattern seen during the early Triassic. Not just because such causes require the release of five times as much methane as postulated for PETM, but whether it should also be buried back at an unrealistic high level to account for the rapid increase in 13 C/ 12 C ratio (episode high positive ? 13 C) throughout the initial Triass before being released several times.
Anoxia Edit
Evidence for broad ocean anoxia (severe oxygen deprivation) and euxinia (presence of hydrogen sulphide) are found from the Late Permian to the Early Triassic. In most of the Tethys and Panthalassic Oceans, evidence for anoxia, including subtle laminate in sediments, small pyrite framboids, high uranium/thorium ratios, and biomarkers for green sulfur bacteria, appears in extinction events. However, in some sites, including Meishan, China, and eastern Greenland, evidence of anoksia precedes extinction. Biomarkers for green sulfur bacteria, such as isorenieratane, diagenetic products of isorenieratene, are widely used as indicators of the euxinia photon zone because green sulfur bacteria require sunlight and hydrogen sulfide to survive. Their abundance in sediments from the P-T boundary indicates hydrogen sulfide is present even in shallow waters.
The spread of toxins, water that lacks oxygen will damage marine life, resulting in widespread death. The ocean chemical model shows that anoxia and euxinia will be closely related to hypercapnia (high levels of carbon dioxide). This suggests that the poisoning of hydrogen sulfide, anoxia, and hypercapnia act together as a mechanism of killing. Hypercapnia most explains the selectivity of extinction, but anoxia and euxinia may contribute to the high mortality of the event. Persistence of anoxia through the Early Triass may explain the slow recovery of marine life after extinction. The model also shows that anoxic events can cause disastrous hydrogen sulfide emissions into the atmosphere (see below).
The sequence of events leading to an anoxic sea may have been triggered by carbon dioxide emissions from the Siberian Trap eruption. In that scenario, warming from the enhanced greenhouse effect will reduce the oxygen solubility in seawater, causing the oxygen concentration to decrease. Increased weathering of continents by warming and accelerating the water cycle will increase fluctuations in the flow of phosphate rivers into the oceans. Phosphate will support greater primary productivity on the surface of the oceans. Increased production of organic matter will cause more organic matter to sink into the deep ocean, where respiration will further lower the oxygen concentration. Once the anoxia becomes established, it will be sustained by positive feedback because deep water anoxia tends to increase the efficiency of phosphate recycling, leading to higher productivity.
Emissions of hydrogen sulfide Edit
A severe anoxic event at the end of the Permian will allow sulphate reducing bacteria to thrive, causing massive production of hydrogen sulphide in an anoxic ocean. This water enlargement may have released massive hydrogen sulfide emissions into the atmosphere and will poison terrestrial plants and animals and greatly weaken the ozone layer, which exposes much of the remaining life to fatal UV radiation levels. Indeed, the evidence of biomarkers for anaerobic photosynthesis by Chlorobiaceae (green sulfur bacteria) from Late-Permian to Early Triasses suggests that hydrogen sulfide rises into shallow water because the bacterium is confined to the photon zone and uses sulphides as electron donors.
The hypothesis has the advantage of explaining the mass extinction of plants, which will be added to methane levels and vice versa should thrive in the atmosphere with high levels of carbon dioxide. The spore fossils from the Permian end further support the theory: many show defects that may be caused by ultraviolet radiation, which will become stronger after the emission of hydrogen sulfide weakens the ozone layer.
The supercontinent pangea Edit
In the middle of Permian (during the monkey period in the Permian's Permian Cianuralian era), the main continental plates joined, forming a superontontent called Pangea, surrounded by superocean, Panthalassa.
Ocean circulation and atmospheric weather patterns during the mid-Permian produce a seasonal monsoon near the coast and dry climates in the vast interior of the Pangean continent.
The diversity of biologically and productively diverse coastal areas is ecologically shrinking when the super continent is formed. Eliminating a shallow aquatic environment exposes previously protected organisms from rich continental shelves to increase environmental volatility.
After the formation of Pangea (see diagram "The diversity of the genus of the oceans" at the top of this article), the rate of decline in marine life is near the level of disaster; However, the extinction of marine life never reached the mass extinction level of "Big Five".
The Pangea effect on extinction on land is considered less significant. In fact, therapsid progress and increased diversity are associated with the late Permian, when the Pangea global influence is estimated to have reached its peak.
While the Pangea formation is known to have begun a long period of extinction of marine life, the significance of its impact on "Big Dying" and the end of the Permian is uncertain.
Microbe Edit
A hypothesis published in 2014 states that the genus of anaerobic metanogenic archaea known as Methanosarcina is responsible for the event. Three lines of evidence indicate that these microbes acquire new metabolic pathways through gene transfer around that time, enabling them to efficiently metabolize acetate into methane. That will lead to their exponential reproduction, enabling them to rapidly consume large deposits of organic carbon that have been accumulated in marine sediments. The result is a sharp buildup of methane and carbon dioxide in the oceans and Earth's atmosphere, in a way that may be consistent with the notes of 13 C/ 12 isotope. Massive volcanism facilitates this process by releasing large quantities of nickel, a rare metal that is a cofactor for the enzymes involved in producing methane. On the other hand, in the canonical Meishan section, the concentration of nickel rises somewhat after the concentration of ? 13 C starts to fall.
The combination of causes Edit
Possible causes supported by strong evidence appear to illustrate a series of disasters, each worse than the last: the Siberian Trap eruption is bad enough, but because they occur near the coal bed and the continental shelf they also trigger a very large release of carbon dioxide. and methane. The resulting global warming may have caused perhaps the most severe anoxic event in ocean history: according to this theory, the oceans become very anoxic, sulfur-reducing anaerobic organisms dominate the ocean chemistry and cause massive emissions of toxic hydrogen sulfide.
Source of the article : Wikipedia
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