Mass Extinction

Mass extinctions are defined every bit "whatsoever substantial increase in the amount of extinction (lineage termination) suffered past more than ane geographically broad-spread higher taxon during a relatively short interval of geologic time, resulting in an at to the lowest degree temporary decline in their standing multifariousness" (Sepkoski, 1986, p. 278).

From: The Future of the World's Climate (Second Edition) , 2012

Extinction in the Fossil Tape

Jeffrey S. Levinton , in Encyclopedia of Biodiversity (2d Edition), 2013

Causes of Mass Extinctions

Mass extinctions are associated in fourth dimension with major environmental changes. The problem, of course, is that other times of no mass extinction also mark the times of environmental modify, and it is off-white to say that we could not easily predict all mass extinctions with nonfossil data alone. If environmental forcing, which transcends the abilities of species to survive or arrange, is a major cause of mass extinction, what are the factors? Nosotros can list them but finding smoking guns is ofttimes another matter.

1.

Bear upon or a series of impacts of extraterrestrially derived objects.

2.

Volcanism.

3.

Climate alter.

4.

Lowering of sea level, which reduces available habitats for marine species.

v.

Anoxia, particularly transgressive spread of deep-anoxic waters onto the continental shelves.

six.

Marsh gas hydrate release, resulting in extreme global warming.

These causes, stem more than from associations in time betwixt inferred geological events and extinctions, and not from a solid model linking environmental change to extinction. The best instance of the latter is the Permian mass extinction. The vast marine regression may accept been the driving force behind a variety of environmental changes, including a rise in carbon dioxide, which led to increased temperature and oceanic anoxia. At the end of the Permian, bounding main level dropped, perhaps about 200   m, which was followed by a transgressive rising of bounding main level in the Lower Triassic of like magnitude in just ii My. Seasonality and reduction of habitat complication during the regression may also have begotten environmental instability, beyond the adaptive ranges of a number of specialized groups. Robert Berner produced a solid model that demonstrated a remarkable drib in atmospheric oxygen from the terminate of the Permian to the beginning of the Triassic. The drib may have been stimulated past a menstruum of all-encompassing volcanism, which in plow caused dry out climates and the wide-spread drying of the planet, which reduced burial of carbon in swamps and released carbon dioxide to the temper. This might take caused all-encompassing warming and temperature stress. The reduction of oxygen might have been the trigger for extinction both on land and bounding main. If oxygen in the ocean declined, hydrogen sulfide might have appeared, which would be poisonous to nigh marine life. Volcanism might be a minor contribution to climate change at the end of the Permian, considering calculations forestall much of a modify in the large 13C deviations at this time, due to outgassing. However, the extensive volcanism in Siberia might have risen to the surface and heated up carbonates and coal deposits, liberating lethal marsh gas, which might accept triggered extinctions and caused larger xiiiC deviations. The Siberian traps comprehend an enormous area of about two million square kilometers. Paleontologists Norman Newell and Anthony Hallam take implicated sea-level change in a number of extinctions throughout the Mesozoic, only they are likewise often combined with other events, such as bolide impacts, anoxia, and temperature change. Douglas Erwin likened this multicomponent explanation to Murder in the Orient Express past Agatha Christie, where twelve culprits were ultimately found to take conspired to murder the victim. Swell for murder mysteries but maddening for scientific discipline. Even this cast of characters ignores the hypothesis of global cooling triggered by glaciation, but this may exist discounted as the glacial testify can be dated much earlier the extinction begins.

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Volume iii

Grzegorz Racki , in Encyclopedia of Geology (Second Edition), 2021

Abstract

Mass extinction events are considered here to be: (1) biodiversity crises, determined primarily past significantly increased extinction rates, and (2) ecological (or biotic) crises, when the ecosystem consequences of the biospheric perturbation were disproportionately large when compared to the protracted/stepwise biodiversity loss alone. Only the end-Permian and end-Cretaceous mass extinctions were unequivocal mass extinctions sensu stricto. The end-Ordovician global event was only a major biodiversity crisis, whereas the Late Devonian and end-Triassic extinctions were major ecological (or biotic) crises. In the causal context, the terminate-Cretaceous catastrophe could have been acquired past the impact of a giant meteorite, but most probably this was just a concluding step leading to the collapse of the biosphere, influenced earlier past Deccan trap volcanism. Four other mass extinctions are more than (Mesozoic) or less (Paleozoic) certainly connected with Earth-leap destructive factors, with big igneous provinces as a leading proposed trigger. The volcanic greenhouse/icehouse scenario has been updated and is supported by recently discovered mercury anomalies. A wide spectrum of killing factors related to volcanic cataclysm, and augmented by non-volcanic factors, has operated inside a totally different fourth dimension scale. The concrete interrelationships and feedbacks were certainly specific for each of the mass extinctions, resulting in their inhomogeneity.

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Mammals (Pre-Quaternary), Extinctions of

William A. Clemens , in Encyclopedia of Biodiversity (Second Edition), 2013

Temporal and Biogeographic Scales of Mass Extinctions

Mass extinctions were defined subjectively equally short periods of World history during which rates of extinction reached exceptionally high levels in widespread areas. In evolutionary terms, how short is short? In studies of recent extinctions in which events are followed on an ecological timescale, short periods of time are measured in terms of years, decades, centuries, or possibly a millennium or ii. A recent compilation of recent estimated durations of the last three of the "Big Five" mass extinctions revealed values every bit much every bit 8.iii  Ma to as short as less than a twelvemonth (Barnosky et al., 2011).

Current radiometric methods for determining ages and durations of pre-Quaternary events lack the degree of resolution plant in ecological studies of the modern biota. For example, using the 40Ar/39Ar method of age determination, which is one of the most precise methods of radiometric age determination available for pre-Quaternary deposits, the age of the Cretaceous–Third boundary, as recognized in nonmarine sediments in eastern Montana, is placed at 65.58±0.04   Ma (Wilson, 2005). Equally data on extinctions of Cretaceous lineages of nonmarine and marine organisms are collected and correlated, all extinction events that occurred within an interval of 80,000   years would necessarily exist treated as having occurred simultaneously. Recognition of the part of curt-term modifications of the biota on an ecological timescale and their consequences in terms of background and mass extinctions on a geological timescale remains a major challenge.

In comparing to the fossil record of marine invertebrates, which is the foundation for studies of the role of mass extinctions in evolution, the fossil record of terrestrial vertebrates is much more than limited, especially in its biogeographic coverage. For case, detailed records of mammalian evolution across the Cretaceous–3rd boundary are limited to sites in the Western Interior of North America (Archibald, 2011). Meaning gaps in the fossil records of mammalian evolution in Eurasia and the continents of the Southern Hemisphere narrate this interval. I outcome of these gaps is the uncertainty in determining the origins of mammalian groups that appear presently subsequently a mass extinction event. Were they descendants of a few local survivors or immigrants from another less impacted and yet to be sampled area?

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Volume iii

Matthew E. Clapham , in Encyclopedia of Geology (2nd Edition), 2021

Implications for Hyperthermals

The EPME shared many similarities with the end-Triassic mass extinction and the smaller Guadalupian and Toarcian extinctions. Why was the EPME, at least in the oceans, more than severe than those other crises? Why did other hyperthermals, such equally the PETM, trigger just limited extinction? This question is i of the most heady ongoing problems in the report of extinctions, and is unlikely to have a uncomplicated solution. It seems likely that the total magnitude of environmental modify was greater during the EPME, at least as inferred from geochemical proxy records. Information technology is less clear, however, whether the rate of environmental disruption was also more than rapid during the EPME. Organisms are able to acclimate or adapt to withstand stressful atmospheric condition, just faster rates of change may overwhelm those capabilities. However, reconstructing the rate of environmental change during deep-time extinctions, especially at timescales relevant to biological adaptation, is extremely challenging. Other differences in the Earth system may explain some of the dissimilar outcomes. The mid-Mesozoic development of a deep-sea reservoir of carbonate sediment would have reduced fluctuations in ocean chemistry during hyperthermals, for instance. Finally, successive extinctions had progressively eliminated marine organisms that were most vulnerable to hyperthermals, potentially reducing the consequences of geologically-younger events. The severity of the cease-Permian mass extinction likely arose from an unfortunate confluence of these factors, only agreement why environmental perturbation leads to extinction is crucial for predicting the consequences of hyperthermals, including the ongoing hyperthermal driven by anthropogenic climatic change.

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Biodiversity

R. Wagler , in Encyclopedia of the Anthropocene, 2018

Abstract

There have been 5 past mass extinctions during the history of Earth. Nosotros take entered a 6th mass extinction. The 6th mass extinction (likewise referred to as the Anthropocene extinction) is an ongoing current event where a big number of living species are threatened with extinction or are going extinct because of the environmentally destructive activities of humans. This article presents an overview of Earth'southward five past mass extinctions, an overview of the electric current 6th mass extinction, electric current and future rates of species extinction associated with the ongoing 6th mass extinction, and past and present human activities associated with the 6th mass extinction.

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Mammals (Pre-Quaternary), Extinctions of

W.A. Clemens , in Encyclopedia of Biodiversity, 2001

II.C. Temporal Scale of Mass Extinctions

Mass extinctions were intentionally defined subjectively as brusk periods of Earth history during which rates of extinction reached uncommonly high levels. In geological terms, how short is brusk? In studies of recent extinctions in which events are followed on an ecological timescale, short periods of time are measured in terms of years, decades, centuries, or perchance a millennium or ii. Current radiometric methods for determining ages and durations of pre-Quaternary events lack this level of resolution. For example, using the fortyAr/39Ar method of historic period determination, which is the most precise method of radiometric historic period conclusion available for pre-4th deposits, the age of the Cretaceous-Tertiary boundary is placed at 65.16 ± 0.04 Ma. Every bit information on extinctions of Cretaceous lineages of marine and nonmarine organisms are collected and correlated, all extinction events that occurred within an interval of 80,000 years would necessarily be treated as having occurred simultaneously. The farther one goes dorsum in World history, the longer the error bars get; for example, some paleontologists currently contend that the extinctions of lineages that contain the Permian-Triassic mass extinction might take occurred over an interval of 1 or two 1000000 years.

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Volume iii

Spencer G. Lucas , in Encyclopedia of Geology (Second Edition), 2021

Ecological Severity of the Extinctions

Mass extinctions are almost often evaluated in terms of biodiversity crashes. However, they take also been analyzed in terms of their ecological severity. In a widely cited scheme of ecological severity, the marine TJB extinction was evaluated every bit category IIa and the nonmarine TJB extinction as category I or IIa. Category I indicates that ecosystems before the extinction were replaced past new ecosystems post-extinction, whereas category IIa indicates that the extinctions caused the permanent loss of major ecosystem components.

Rating the TJB marine extinction every bit category IIa was largely based on a perceived global reef extinction. However, every bit discussed above, this disruption was not demonstrably global, and information technology was definitely temporary. Therefore, the TJB marine extinction should be downgraded to category IIb, which means that the disruption was temporary; i.east., the reef ecosystem re-established itself afterwards a hiatus.

It has long been claimed that the TJB transition involved a rapid ecological replacement of Triassic "mammal-similar reptiles" (synapsids) and rhynchosaurs past dinosaurs. However, rhynchosaurs and dicynodont synapsids are known from strata no younger than Norian. The other principal group of Late Triassic synapsids, the cynodonts, were of low diverseness after the Carnian (run into above). The oldest record of dinosaur body fossils is Carnian, and dinosaurs began to diversify essentially in some parts of Pangea past the late Norian. Thus, the ecological severity of the end-Triassic tetrapod extinction is relatively low (Category IIb), and there are also no extensive institute extinctions across the TJB. Clearly, the terrestrial ecosystem was disrupted across the TJB, but it was non a severe disruption.

Trophic systems in the body of water and on the land did not collapse across the TJB. There was no mass extinction of the oceanic plankton across the TJB, so there also was no collapse of marine food chains. Similarly, the lack of a mass extinction of land plants makes it difficult to envision a plummet of the metazoan trophic structure that relied on plants as the principal sources of food.

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The Big Five or Six or More …

Steve Webb , in Corridors to Extinction and the Australian Megafauna, 2013

Numerous mass extinctions have taken identify during the last billion years. No book about extinction can ignore these so the showtime affiliate of this book briefly describes them. It is soon credible that separating some of these events from each other is rather hard. Extinction is ongoing and the list seems to propose that that process sometimes accelerates and then goes very quite. Considering of that this affiliate likewise describes groundwork extinction, the benefits of extinction, why animals go extinct and the fact that without the many extinctions of the past we would not be here.

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Earth'due south Temper, Hydrosphere, and Biosphere

Kent C. Condie , in Earth as an Evolving Planetary System (Second Edition), 2011

Episodic Distributions

8 mass extinctions are recognized in the Phanerozoic, and the aforementioned peaks are institute for terrestrial and marine organisms, indicating that the major extinctions affected organisms on land and in the bounding main at the same time ( Sepkoski, 1989; Benton, 1995; Foote, 2003) (Figure half-dozen.26). The Late Carboniferous, Belatedly Jurassic, and Early on Cretaceous extinctions are more than prominent for terrestrial than marine organisms. V major mass extinctions are recognized: Late Ordovician, Late Devonian, Late Permian, Late Triassic, and Belatedly Cretaceous (Effigy 6.27). Of these, the Permian extinction charge per unit is highest, with a mean family unit extinction rate of 61% for all life, 63% for terrestrial organisms, and 49% for marine organisms (Benton, 1995). Peaks in origination of species more often than not follow extinction peaks by <30   Ma, which appears to reflect the fourth dimension necessary to fill abandoned ecological niches with new species (Effigy 6.26). Extinction events tend to occur during times of high preservation potential, whereas origination events following these extinctions are more likely to occur at times that are more poorly represented by the fossil record (Foote, 2003).

Figure 6.26. Rates of origination and extinction of marine animals during the Phanerozoic.

 Modified afterwards Foote (2003).

Figure 6.27. Major mass extinctions during the Phanerozoic showing number of families as a measure out of biologic diverseness.

 From Metcalf &amp; Isozaki (2009), courtesy of Ian Metcalf.

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Book 5

Simone Fattorini , in Encyclopedia of Geology (2nd Edition), 2021

Eocene–Oligocene Mass Extinction

A mass extinction occurred at the Eocene–Oligocene boundary (33.9  mya) in association with global cooling. This mass extinction event is known in Europe as the Grande Coupure ("the bully intermission," an expression coined by the Swiss paleontologist Hans Georg Stehlin in 1910 to indicate a dramatic turnover of European mammalian animate being; a comparable turnover in Asian brute is called the "Mongolian Remodeling"). About one-half of the mammal genera became extinct inside a million years, including the terminal of the ancient cetaceans (Archaeoceti). Evidence of a bolide impact about 35.5   mya at Chesapeake Bay (Virginia, USA) has been suggested equally an extraterrestrial cause. Some other bear upon, the source of the Popigai crater in northern Siberia, as well occurred approximately 35   mya. Whether these impacts occurred simultaneously or within a few hundred thousand years, either would have been sufficiently catastrophic to take caused a mass extinction with (1) an initial concrete disruption of large regions; (2) climatic cooling for several years due to stratospheric dust, which likewise caused a photosynthetic decline; and (3) perhaps longer-term warming if there was a carbon dioxide release. Information technology has been besides proposed that climate cooling was due to a decrease in atmospheric carbon dioxide, which slowly declined in the Mid- to Late Eocene and mayhap reached some threshold approximately 34 million years agone, thus enabling a rapid buildup of a permanent water ice canvass on the Antarctic continent. Other explanations evoke large-scale volcanic activity (mayhap past the Ethiopian Traps). Since glacial growth led to a autumn in sea level, land-bridges formed between Due north America and Asia, likewise as Northward and South America. These connections would have allowed many species to disperse into new areas, thus leading to new negative interspecific relationships that might have contributed to the extinction result.

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