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Encyclopedia > Extinction event

An extinction event (also known as: mass extinction; extinction-level event, ELE) occurs when there is a sharp decrease in the number of species in a relatively short period of time. Mass extinctions affect most major taxonomic groups present at the time — birds, mammals, reptiles, amphibians, fish, invertebrates and other simpler life forms. They may be caused by one or both of: In biology, a species is one of the basic units of biodiversity. ... Look up taxonomy in Wiktionary, the free dictionary. ... For other meanings of bird, see bird (disambiguation). ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the production of milk in female mammary glands and the presence of hair, three middle ear bones used in hearing, and a neocortex region in the... Subclasses Anapsida Diapsida Synonyms Reptilia Laurenti, 1768 Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane, and members of the class Sauropsida. ... Subclasses and Orders    Order Temnospondyli - extinct Subclass Lepospondyli - extinct Subclass Lissamphibia    Order Anura    Order Caudata    Order Gymnophiona Amphibians (class Amphibia; from Greek αμφις both and βιος life) are a taxon of animals that include all living tetrapods (four-legged vertebrates) that do not have amniotic eggs, are ectothermic (term for the animals... A giant grouper at the Georgia Aquarium Fish are aquatic vertebrates that are typically cold-blooded; covered with scales, and equipped with two sets of paired fins and several unpaired fins. ... Invertebrate is a term that describes any animal without a spinal column. ...

Based on the fossil record , the background rate of extinctions on Earth is about two to five taxonomic families of marine invertebrates and vertebrates every million years.[2] Marine fossils are generally used to measure extinction rates because they are more plentiful and cover a longer time span than fossils of land organisms. The Dodo, shown here in illustration, is an often-cited[1] example of modern extinction. ... In biology, a species is one of the basic units of biodiversity. ... Charles Darwins first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837) Speciation is the evolutionary process by which new biological species arise. ... The Dodo, shown here in illustration, is an often-cited[1] example of modern extinction. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... Taxonomy, sometimes alpha taxonomy, is the science of finding, describing and naming organisms, thus giving rise to taxa. ... In biological classification, family (Latin: familia, plural familiae) is 1) a rank or 2) a taxon in that rank. ... Invertebrate is a term that describes any animal without a spinal column. ... Classes and Clades See below Male and female Superb Fairy-wren Vertebrates are members of the subphylum Vertebrata (within the phylum Chordata), specifically, those chordates with backbones or spinal columns. ...

Apparent extinction intensity, i.e. the fraction of genera going extinct at any given time, as reconstructed from the fossil record. (Graph not meant to include recent epoch of Holocene extinction event)
Apparent extinction intensity, i.e. the fraction of genera going extinct at any given time, as reconstructed from the fossil record. (Graph not meant to include recent epoch of Holocene extinction event)

Since life began on Earth, several major mass extinctions have significantly exceeded the background extinction rate. Almost as famous as dinosaurs themselves is the fact that they died out in a very short time. Over 90 percent of the organisms that have ever lived are extinct. The most recent one occurred 65 million years ago and has attracted more attention than all others because it finished off the dinosaurs. However, extinction does not occur at an even rate. In the past 550 million years there have been five major extinctions, when over 50 percent of animal species died. Although there probably were mass extinctions in the Archean and Proterozoic, it is only during the Phanerozoic Eon that the evolution of organisms with hard body parts has provided a sufficient fossil record from which to make a systematic study of extinction patterns. Image File history File links Description Total Phanerozoic biodiversity during the same interval. ... Image File history File links Description Total Phanerozoic biodiversity during the same interval. ... For other uses of the word, please see Genus (disambiguation). ... It has been suggested that this article or section be merged into Fossil. ... The Dodo, a bird of Mauritius, became extinct during the mid-late 17th century after humans destroyed the forests where the birds made their homes and introduced animals that ate their eggs. ... The Archean is a geologic eon; it is a somewhat antiquated term for the time span between 2500 million years before the present and 3800 million years before the present. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... The Phanerozoic (occasionally Phaenerozoic) Eon is the period of geologic time during which abundant animal life has existed. ... In general usage, an eon (sometimes spelled aeon) is a very long period of time. ... This article is about evolution in biology. ... It has been suggested that this article or section be merged into Fossil. ...


Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty.These differences stem primarily from: (a) the threshold chosen for describing an extinction event as "major"; (b) what set of data one chooses as the measure of past diversity.

Contents

Major extinction events

The classical "Big Five" mass extinctions identified by Jack Sepkoski and David M. Raup in their 1982 paper are widely agreed upon as some of the most significant: End Ordovician, Late Devonian, End Permian, End Triassic, and End Cretaceous.[3] J. John Sepkoski Jr. ... David M. Raup is a University of Chicago paleontologist. ... The Ordovician-Silurian extinction event, labeled End O here. ... Comparison of the three episodes of extinction in the Late Devonian (Late D) to other mass extinction events in Earths history. ... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ... Comparison of the intensity of the T-J extinction event, labeled here End Tr to other extinction events in the last 500 million years. ... Badlands near Drumheller, Alberta where erosion has exposed the KT boundary. ...


These and a selection of other extinction events are outlined below. The articles about individual mass extinctions describe their effects in more detail and discuss theories about their causes.

  1. 488 million years ago — a series of mass extinctions at the Cambrian-Ordovician transition (the Cambrian-Ordovician extinction events) eliminated many brachiopods and conodonts and severely reduced the number of trilobite species.
  2. 444 million years ago — at the Ordovician-Silurian transition two Ordovician-Silurian extinction events occurred, and together these are ranked by many scientists as the second largest of the five major extinctions in Earth's history in terms of percentage of genera that went extinct.
  3. 360 million years ago — near the Devonian-Carboniferous transition (the Late Devonian extinction) a prolonged series of extinctions led to the elimination of about 70% of all species. This was not a sudden event — the period of decline lasted perhaps as long as 20 million years, and there is evidence for a series of extinction pulses within this period.
  4. 251 million years ago — at the Permian-Triassic transition Earth's largest extinction (the P/Tr or Permian-Triassic extinction event) killed 53% of marine families, 84% of marine genera, about 96% of all marine species and an estimated 70% of land species (including plants, insects, and vertebrate animals). The "Great Dying" had enormous evolutionary significance: on land it ended the dominance of the mammal-like reptiles and created the opportunity for archosaurs and then dinosaurs to become the dominant land vertebrates; in the seas the percentage of animals that were sessile dropped from 67% to 50%.
    The whole of the late Permian was a difficult time for at least marine life - even before the "Great Dying", the diagram shows a late-Permian level of extinction large enough to qualify for inclusion in the "Big Five".
  5. 200 million years ago — at the Triassic-Jurassic transition (the Triassic-Jurassic extinction event) about 20% of all marine families as well as most non-dinosaurian archosaurs, most therapsids, and the last of the large amphibians were eliminated.
  6. 65 million years ago — at the Cretaceous-Paleogene transition (the K/T or Cretaceous-Tertiary extinction event) about 50% of all species became extinct. It has great significance for humans because it ended the reign of the dinosaurs and opened the way for mammals to become the dominant land vertebrates; and in the seas it reduced the percentage of sessile animals again, to about 33%. The K/T extinction was rather uneven — some groups of organisms became extinct, some suffered heavy losses and some appear to have got off relatively lightly.
  7. Present day — the Holocene extinction event. A 1998 survey by the American Museum of Natural History found that 70% of biologists view the present era as part of a mass extinction event, possibly one of the fastest ever. Some, such as E. O. Wilson of Harvard University, predict that man's destruction of the biosphere could cause the extinction of one-half of all species in the next 100 years. Research and conservation efforts, such as the IUCN's annual "Red List" of threatened species, all point to an ongoing period of enhanced extinction, though some offer much lower rates and hence longer time scales before the onset of catastrophic damage. The extinction of many megafauna near the end of the most recent ice age is also sometimes considered a part of the Holocene extinction event.[4] Some paleontologists, however, question whether the available data support a comparison with mass extinctions in the past.[5]

The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... The Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era. ... The Cambrian-Ordovician extinction event occured approximately 488 million years ago, an extinction event that eliminated many brachiopods and conodonts and severely reduced the number of trilobite species. ... Subphyla and classes See Classification Brachiopods (from Latin brachium, arm + New Latin -poda, foot) are a phylum of animals. ... Conodonts are extinct worm-like forms with distinctive conical or multi-denticulate teeth made of apatite (calcium phosphate). ... Orders Agnostida Nectaspida Redlichiida Corynexochida Lichida Phacopida Subclass: Librostoma Proetida Asaphida Harpetida Ptychopariida For the robot vacuum cleaner, see Electrolux Trilobite. ... The Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era. ... The Silurian is a major division of the geologic timescale that extends from the end of the Ordovician period, about 443. ... The Ordovician-Silurian extinction event, labeled End O here. ... For other uses of the word, please see Genus (disambiguation). ... Artists illustration of a Devonian scene. ... The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359. ... Comparison of the three episodes of extinction in the Late Devonian (Late D) to other mass extinction events in Earths history. ... The Permian is a geologic period that extends from about 299. ... The Triassic is a geologic period that extends from about 251 ± 0. ... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ... For other uses of the word, please see Genus (disambiguation). ... Mammal-like reptiles is a term used to describe the prehistoric animals that appear to be the reptilian ancestors of mammals. ... -1... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ... Look up sessile in Wiktionary, the free dictionary. ... The Triassic is a geologic period that extends from about 251 ± 0. ... The Jurassic Period is a major unit of the geologic timescale that extends from about 199. ... Comparison of the intensity of the T-J extinction event, labeled here End Tr to other extinction events in the last 500 million years. ... -1... Suborders Biarmosuchia Dinocephalia Eotheriodontia Anomodontia Gorgonopsia Therocephalia Cynodontia Therapsids, previously known as the mammal-like reptiles, are an order of synapsids. ... For other uses, see Amphibian (disambiguation). ... The Cretaceous Period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic Period (i. ... Paleogene (alternatively Palaeogene) period is a unit of geologic time that began 65 and ended 23 million years ago. ... Badlands near Drumheller, Alberta where erosion has exposed the KT boundary. ... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the production of milk in female mammary glands and the presence of hair, three middle ear bones used in hearing, and a neocortex region in the... Look up sessile in Wiktionary, the free dictionary. ... The Dodo, a bird of Mauritius, became extinct during the mid-late 17th century after humans destroyed the forests where the birds made their homes and introduced animals that ate their eggs. ... Edward Osborne Wilson (b. ... Harvard University (incorporated as The President and Fellows of Harvard College) is a private university in Cambridge, Massachusetts, USA and a member of the Ivy League. ... A false-color composite of global oceanic and terrestrial photoautotroph abundance, from September 1997 to August 2000. ... The World Conservation Union or International Union for Conservation of Nature and Natural Resources (IUCN) is an international organization dedicated to natural resource conservation. ... The IUCN Red List of Threatened Species (also known as the IUCN Red List and Red Data List), created in 1963, is the worlds most comprehensive inventory of the global conservation status of plant and animal species. ... The mammoth, an extinct genus of megafauna. ... The Holocene epoch is a geological period that extends from the present day back to about 10,000 radiocarbon years, approximately 11,430 ± 130 calendar years BP (between 9560 and 9300 BC). ... A paleontologist carefully chips rock from a column of dinosaur vertebrae. ...

Evolutionary importance of mass extinctions

Mass extinctions have sometimes accelerated the evolution of life on earth. Evolution is a dynamic process and there is a constant turnover of species. Herbivorous and carnivorous dinosaurs were badly affected, as were lizards, sharks, marsupials, and a range of marine organisms. However, other mammals, crocodiles, turtles, frogs, salamanders, and numerous other marine organisms survived relatively unscathed. Evolution flows through time, creating and losing species. Lungfish first evolved 400 million years ago, sharks 300 million years ago, and sturgeons 200 million years ago. When dominance of particular ecological niches passes from one group of organisms to another, it is rarely because the new dominant group is "superior" to the old and usually because an extinction event eliminates the old dominant group and makes way for the new one.[6] This article is about the tv programme Life on Earth. ...


For example mammaliformes ("almost mammals") and then mammals existed throughout the reign of the dinosaurs, but could not compete for the large terrestrial vertebrate niches which dinosaurs monopolized. The end-Cretaceous mass extinction removed the non-avian dinosaurs and made it possible for mammals to expand into the large terrestrial vertebrate niches. Clades Adelobasileus Sinoconodon Morganucodonta Docodonta Hadrocodium Mammalia Mammaliaformes is a clade that contains the mammals and their closest extinct relatives. ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the production of milk in female mammary glands and the presence of hair, three middle ear bones used in hearing, and a neocortex region in the... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ... Badlands near Drumheller, Alberta where erosion has exposed the KT boundary. ...


On the other hand many groups which survive mass extinctions do not recover in numbers or diversity, and many of these go into long-term decline.[7] This phenomenon is known as "Dead Clade Walking". So most "what died and what survived" analyses understate the full effect of mass extinctions. Dead Clade Walking refers to the fact that some groups of organisms which survive mass extinctions either become extinct a few million years after the mass extinction or fail to recover in numbers and diversity. ...


Is the frequency of extinctions decreasing?

The diagram at the top of this page appears to show that:

  • The gaps between mass extinctions are becoming longer.
  • The average and background rates of extinction are decreasing.

The idea that mass extinctions are becoming less frequent is rather speculative - from a statistical point of view a sample of about 10 extinction events is too small to be a reliable sign of any actual trend. But the average and background rates of extinction are based on hundreds of samples over a period of 550M years, so the apparent decrease in these rates is statistically significant and needs to be explained. A graph of a Normal bell curve showing statistics used in educational assessment and comparing various grading methods. ...


Both of these phenomena could be explained by one or more of:[8]

  • Reasonably complete fossils are very rare, most extinct organisms are represented only by partial fossils, and complete fossils are rarest in the oldest rocks. So paleontologists have mistakenly assigned parts of the same organism to different genera which were often defined solely to accommodate these finds (the story of Anomalocaris is a good example). The risk of this mistake is higher for older fossils because these are often unlike parts of any living organism. Many of the "superfluous" genera are represented by fragments which are not found again and the "superfluous" genera appear to become extinct very quickly.
  • Martin (1994, 1996) has argued that the oceans have become more hospitable to life over the last 500M years and less vulnerable to mass extinctions: dissolved oxygen became more widespread and penetrated to greater depths; the development of life on land reduced the run-off of nutrients and hence the risk of eutrophication and anoxic events; and marine ecosystems became more diversified so that food chains were less likely to be disrupted.[9][10]

FOSSIL is a standard for allowing serial communication for telecommunications programs under DOS. FOSSIL is an acronym for Fido Opus Seadog Standard Interface Layer. ... For other uses of the word, please see Genus (disambiguation). ... Species  ? Image of the first complete Anomalocaris fossil found, residing in the Royal Ontario Museum Anomalocaris (unusual shrimp) is an extinct genus of anomalocarids, which are, in turn, thought to be closely related to the Arthropoda. ... Oxygen saturation or dissolved oxygen (DO) is a measure of amount of oxygen dissolved in a given medium. ... Eutrophication is a change in an ecosystem caused by increased growth of a species. ... Oceanic Anoxic Events occur when the Earths oceans become completely depleted of O2 below the surface levels. ... This article or section does not cite any references or sources. ...

Causes of mass extinction

There is still debate about the causes of all mass extinctions before the Holocene. The Dodo, a bird of Mauritius, became extinct during the mid-late 17th century after humans destroyed the forests where the birds made their homes and introduced animals that ate their eggs. ...


Looking for the causes of particular mass extinctions

A good theory for a particular mass extinction should: (i) explain all of the losses, not just focus on a few groups (such as dinosaurs); (ii) explain why particular groups of organisms died out and why others survived; (iii) provide killing mechanisms which are strong enough to cause a mass extinction but not a total extinction; (iv) be based on events or processes that can be shown to have happened, not just inferred from the extinction. To understand this event we have to put it in context. Extinction is an integral part of evolution. All creatures eventually die out and this does not imply "failure." There have been over 80 theories suggested to explain the demise of the dinosaurs.


It may be necessary to consider combinations of causes. For example the marine aspect of the end-Cretaceous extinction appears to have been caused by several processes which partially overlapped in time and may have had different levels of significance in different parts of the world.[11] Badlands near Drumheller, Alberta where erosion has exposed the KT boundary. ...


Arens and West (2006) proposed a "press / pulse" model in which mass extinctions generally require 2 types of cause: long-term pressure on the eco-system ("press") and a sudden catastrophe ("pulse") towards the end of the period of pressure.[12] Their statistical analysis of marine extinction rates throughout the Phanerozoic suggested that neither long-term pressure alone nor a catastrophe alone was sufficient to cause a significant increase in the extinction rate. The Phanerozoic (occasionally Phaenerozoic) Eon is the period of geologic time during which abundant animal life has existed. ...


Most widely-supported explanations

Macleod (2001)[13] summarised the relationship between mass extinctions and events which are most often cited as causes of mass extinctions, using data from Courtillot et al (1996),[14] Hallam (1992)[15] and Grieve et al (1996)[16]:

  • Flood basalt events: 11 occurrences, all associated with significant extinctions[17][18] But Wignall (2001) concluded that only 5 of the major extinctions coincided with flood Basalt eruptions and that the main phase of extinctions started before the eruptions.[19]
  • Sea-level falls: 12, of which 7 were associated with significant extinctions.[18]
  • Asteroid impacts producing craters over 100km wide: 1, associated with 1 mass extinction.
  • Asteroid impacts producing craters less than 100km wide: over 50, the great majority not associated with significant extinctions.

The most commonly-suggested causes of mass extinctions are: Moses Coulee showing multiple flood basalt flows of the Columbia River Basalt Group. ...

  1. Flood basalt events
    The formation of large igneous provinces by flood basalt events could have: produced dust and particulate aerosols which inhibited photosynthesis and thus caused food chains to collapse both on land and at sea; emitted sulfur oxides which were precipitated as acid rain and poisoned many organisms, contributing further to the collapse of food chains; emitted carbon dioxide and thus caused sustained global warming once the dust and particulate aerosols dissipated. Flood basalt events occur as pulses of activity punctuated by dormant periods. As a result they are likely to cause the climate to oscillate between cooling and warming, but with an overall trend towards warming as the carbon dioxide they emit can stay in the atmosphere for hundreds of years.
    Various scientists have suggested that massive volcanism caused or contributed to the End-Cretaceous, End-Permian, End Triassic and End Jurassic extinctions.
  2. Sea-level falls
    These are often clearly marked by world-wide sequences of contemporaneous sediments which show all or part of a transition from sea-bed to tidal zone to beach to dry land - and where there is no evidence that the rocks in the relevant areas were raised by geological processes such as orogeny. Sea-level falls could reduce the continental shelf area (the most productive part of the oceans) sufficiently to cause a marine mass extinction, and could disrupt weather patterns enough to cause extinctions on land.
    But sea-level falls are very probably the result of other events, such as sustained global cooling or the sinking of the mid-ocean ridges.
    Sea-level falls are associated with most of the mass extinctions, including all of the "Big Five" — End-Ordovician, Late Devonian, End-Permian, End-Triassic, and End-Cretaceous.
  3. Impact events
    The impact of a sufficiently large asteroid or comet could have caused food chains to collapse both on land and at sea by producing dust and particulate aerosols and thus inhibiting photosynthesis. If it hit sulfur-rich rocks, it could also have emitted sulfur oxides which were precipitated as acid rain and poisoned many organisms — contributing further to the collapse of food chains. Some scientists have suggested that impacts could also have caused megatsunamis and / or global forest fires, but these ideas are now regarded as exaggerations.
    Only the end-Cretaceous extinction is associated with strong evidence of such an impact, but that impact is easily the largest for which there is strong evidence.
  4. Sustained global cooling
    This could: kill many polar and temperate species and force others to migrate towards the equator; reduce the area available for tropical species; often make the Earth's climate more arid on average, mainly by locking up more of the planet's water in ice and snow. The glaciation cycles of the current ice age are believed to have had only a very mild impact on biodiversity, so the mere existence of a significant cooling is not sufficient on its own to explain a mass extinction.
    It has been suggested that global cooling caused or contributed to the End-Ordovician, Permian-Triassic, Late Devonian extinctions, and possibly others.
    Note: this item is labelled "sustained global cooling" to distinguish it from the temporary climatic effects of flood basalt events or impacts.
  5. Sustained global warming
    This would have the opposite effects: expand the area available for tropical species; kill temperate species or force them to migrate towards the Poles (or perish); possibly cause severe extinctions of polar species; often make the Earth's climate wetter on average, mainly by melting ice and snow and thus increasing the volume of the water cycle. It might also cause anoxic events in the oceans (see below).
    The most dramatic example of sustained warming is the Paleocene-Eocene Thermal Maximum, which was associated with one of the smaller mass extinctions.
  6. Clathrate gun hypothesis
    Clathrates are composites in which a lattice of one substance forms a cage round another. Methane clathrates (in which water molecules are the cage) form on continental shelves. These clathrates are likely to break up rapidly and release the methane if the temperature rises quickly or the pressure on them drops quickly - for example in response to sudden global warming or a sudden drop in sea level or even earthquakes. Methane is a much more powerful greenhouse gas than carbon dioxide, so a methane eruption ("clathrate gun") could cause rapid global warming or make it much more severe if the eruption was itself caused by global warming.
    The most likely signature of such a methane eruption would be a sudden decrease in the ratio of carbon-13 to carbon-12 in sediments, since methane clathrates are low in carbon-13; but the change would have to be very large, as other events can also reduce the percentage of carbon-13.[20]
    It has been suggested that "clathrate gun" methane eruptions were involved in the end-Permian extinction and in the Paleocene-Eocene Thermal Maximum, which was associated with one of the smaller mass extinctions.
  7. Anoxic events
    These are situations in which the upper and even the middle layers of the ocean become deficient or totally lacking in oxygen. Their causes are complex and controversial, but all known instances are associated with severe and sustained global warming, mostly caused by massive sustained volcanism.
    It has been suggested that anoxic events caused or contributed to the late Devonian, Permian-Triassic and Triassic-Jurassic extinctions. On the other hand there are widespread black shale beds from the mid-Cretaceous which indicate anoxic events but are not associated with mass extinctions.
  8. Hydrogen sulfide emissions from the seas
    Kump, Pavlov and Arthur (2005) have proposed that during the Permian-Triassic extinction the warming also upset the oceanic balance between photosynthesising plankton and deep-water sulfate-reducing bacteria, causing massive emissions of hydrogen sulfide which poisoned life on both land and sea and severely weakened the ozone layer, exposing much of the life that still remained to fatal levels of UV radiation.[21][22][23]
  9. Oceanic overturn
    This is a disruption of thermo-haline circulation which lets surface water (which is more saline than deep water because of evaporation) sink straight down, bringing anoxic deep water to the surface and therefore killing most of the oxygen-breathing organisms which inhabit the surface and middle depths. It may occur either at the beginning or the end of a glaciation, although an overturn at the start of a glaciation is more dangerous because the preceding warm period will have created a larger volume of anoxic water. [24]
    Unlike other oceanic catastrophes such as regressions (sea-level falls) and anoxic events, overturns do not leave easily-identified "signatures" in rocks and are theoretical consequences of researchers' conclusions about other climatic and marine events.
    It has been suggested that oceanic overturn caused or contributed to the late Devonian and Permian-Triassic extinctions.
  10. A nearby nova, supernova or gamma ray burst
    A nearby gamma ray burst (less than 6000 light years distance) could sufficiently irradiate the surface of the Earth to kill organisms living there and destroy the ozone layer in the process. From statistical arguments, approximately 1 gamma ray burst would be expected to occur in close proximity to Earth in the last 540 million years. A proposal that a supernova or gamma ray burst had caused a mass extinction would also have to be backed up by astronomical evidence of such an explosion at the right place and time.
    It has been suggested that a supernova or gamma ray burst caused the End-Ordovician extinction.
  11. Continental drift
    Movement of the continents into some configurations can cause or contribute to extinctions in several ways: by initiating or ending ice ages; by changing ocean and wind currents and thus altering climate; by opening seaways or land bridges which expose previously isolated species to competition for which they are poorly-adapted (for example the extinction of most American marsupials after the creation of a land bridge between North and South America). Occasionally continental drift creates a super-continent which includes the vast majority of Earth's land area, which in addition to the effects listed above is likely to reduce the total area of continental shelf (the most species-rich part of the ocean) and produce a vast, arid continental interior which may have extreme seasonal variations.
    It is widely thought that the creation of the super-continent Pangea contributed to the End-Permian mass extinction. Pangaea was almost fully formed at the transition from mid-Permian to late-Permian, and the "Marine genus diversity" diagram at the top of this article shows a level of extinction starting at that time which might have qualified for inclusion in the "Big Five" if it were not overshadowed by the "Great Dying" at the end of the Permian.
  12. Plate tectonics
    This is the mechanism which drives many of the possible causes of mass extinctions, especially volcanism and continental drift. So it is implicated in many extinctions, but in each case it is necessary to specify which manifestations of plate tectonics were involved.

Many other hypotheses have been proposed, such as the spread of a new disease or simple out-competition following an especially successful biological innovation. But all have been rejected, usually for one of the following reasons: they require events or processes for which there is no evidence; they assume mechanisms which are contrary to the available evidence; they are based on other theories which have been rejected or superseded. Moses Coulee showing multiple flood basalt flows of the Columbia River Basalt Group. ... A large igneous province (LIP) is an extensive region of basalts resulting from flood basalt volcanism. ... Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... This article or section does not cite any references or sources. ... The term acid rain also known as acid precipitation is commonly used to mean the deposition of acidic components in rain, snow, dew, or dry particles. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... A schematic representation of the exchanges of energy between outer space, the Earths atmosphere, and the Earth surface. ... Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... Badlands near Drumheller, Alberta where erosion has exposed the KT boundary. ... The Permian-Triassic extinction event, labeled End P here, is the most significant extinction event in this plot for marine fossiliferous genera. ... Comparison of the intensity of the T-J extinction event, labeled here End Tr to other extinction events in the last 500 million years. ... The Triassic-Jurassic extinction events were extinction events. ... // Orogeny (Greek for mountain generating) is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within... The tectonic plates of the world were mapped in the second half of the 20th century. ... The Ordovician-Silurian extinction event, labeled End O here. ... Comparison of the three episodes of extinction in the Late Devonian (Late D) to other mass extinction events in Earths history. ... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ... Comparison of the intensity of the T-J extinction event, labeled here End Tr to other extinction events in the last 500 million years. ... Badlands near Drumheller, Alberta where erosion has exposed the KT boundary. ... Artists impression of a major impact event. ... This article or section does not cite any references or sources. ... Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... The term acid rain also known as acid precipitation is commonly used to mean the deposition of acidic components in rain, snow, dew, or dry particles. ... Megatsunami (often hyphenated as mega-tsunami, also known as iminami or “wave of purification”) is an informal term used mostly by popular media and popular scientific societies to describe a very large tsunami wave beyond the typical size reached by most tsunamis (usually around 10 metres). ... Fire in San Bernardino, California Mountains (image taken from the International Space Station) A wildfire, also known as a forest fire, vegetation fire, grass fire, or bushfire (in Australasia), is an uncontrolled fire in wildland often caused by lightning; other common causes are human carelessness and arson. ... Badlands near Drumheller, Alberta where erosion has exposed the KT boundary. ... The polar circles is a name for the Arctic and the Antarctic Circle. ... In geography, temperate latitudes of the globe lie between the tropics and the polar circles. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ... A noontime scene from the Philippines on a day when the sun is almost directly overhead. ... A glaciation (a created composite term meaning Glacial Period, referring to the Period or Era of, as well as the process of High Glacial Activity), often called an ice age, is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... The Ordovician-Silurian extinction event, labeled End O here. ... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ... Comparison of the three episodes of extinction in the Late Devonian (Late D) to other mass extinction events in Earths history. ... A noontime scene from the Philippines on a day when the sun is almost directly overhead. ... In geography, temperate latitudes of the globe lie between the tropics and the polar circles. ... The movement of water around, over, and through the Earth is called the water cycle. ... Climate change during the last 65 million years. ... The clathrate gun hypothesis states that as sea temperatures rise the sudden release of methane from methane clathrate compounds buried in the seabeds will cause a drastic alteration of the ocean enviornment and the atmosphere of earth, as recent analysis concerning the Permian extinction event indicates may have happened in... A clathrate or clathrate compound is a chemical substance consisting of a Greek klethra, meaning bars (in the sense of a lattice). ... Methane is a chemical compound with the molecular formula CH4. ...  Sediment  Rock  Mantle  The global continental shelf, highlighted in cyan The continental shelf is the extended perimeter of each continent, which is covered during interglacial periods such as the current epoch by relatively shallow seas (known as shelf seas) and gulfs. ... Global mean surface temperatures 1850 to 2006 Mean surface temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980 Global warming is the observed increase in the average temperature of the Earths atmosphere and oceans in recent decades and the projected... A schematic representation of the exchanges of energy between outer space, the Earths atmosphere, and the Earth surface. ... The distribution of stable isotopes and certain elements within a food web make it possible to draw direct inferences regarding diet, trophic level, and subsistence. ... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ... Climate change during the last 65 million years. ... Oceanic Anoxic Events occur when the Earths oceans become completely depleted of O2 below the surface levels. ... Comparison of the three episodes of extinction in the Late Devonian (Late D) to other mass extinction events in Earths history. ... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ... Comparison of the intensity of the T-J extinction event, labeled here End Tr to other extinction events in the last 500 million years. ... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ... The leaf is the primary site of photosynthesis in plants. ... Sulfate-reducing bacteria comprise several groups of bacteria that use sulfate as an oxidizing agent, reducing it to sulfide. ... Hydrogen sulfide (hydrogen sulphide in British English), H2S, is a colorless, toxic, flammable gas that is responsible for the foul odor of rotten eggs and flatulence. ... The ozone layer is the part of the Earths atmosphere which contains relatively high concentrations of ozone (O3). ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... A simplified summary of the path of the Thermohaline Circulation. ... A glaciation (a created composite term meaning Glacial Period, referring to the Period or Era of, as well as the process of High Glacial Activity), often called an ice age, is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. ... Comparison of the three episodes of extinction in the Late Devonian (Late D) to other mass extinction events in Earths history. ... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ... Artists conception of a white dwarf star accreting hydrogen from a larger companion A nova (pl. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... The image above shows the optical afterglow of gamma ray burst GRB-990123 taken on January 23, 1999. ... A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in vacuum in one year. ... The ozone layer is the part of the Earths atmosphere which contains relatively high concentrations of ozone (O3). ... The Ordovician-Silurian extinction event, labeled End O here. ... Plates in the crust of the earth, according to the plate tectonics theory Continental drift refers to the movement of the Earths continents relative to each other. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... Orders Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Sparassodonta (extinct) Marsupials are mammals in which the female typically has a pouch (called the marsupium, from which the name Marsupial derives) in which it rears its young through early infancy. ...  Sediment  Rock  Mantle  The global continental shelf, highlighted in cyan The continental shelf is the extended perimeter of each continent, which is covered during interglacial periods such as the current epoch by relatively shallow seas (known as shelf seas) and gulfs. ... Pangea may refer to: a common alternative spelling of the name Pangaea given to the supercontinent that is believed to have existed during the Paleozoic and Mesozoic eras Pangea, a geology equipment supplier/developer of mineralogical testing equipment Pangea (cable system), a submarine telecommunications cable system connecting the Netherlands and... The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... The term disease refers to an abnormal condition of an organism that impairs function. ...


Postulated extinction cycles

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Please help Wikipedia by adding references. See the talk page for details.

It has been suggested by several sources that biodiversity and/or extinction events may be influenced by cyclic processes. The best-known of these claims is the 26 to 30 million year viral cycle in extinctions proposed by Raup and Sepkoski (1986). More recently, Rohde and Muller (2005) have suggested that biodiversity fluctuates primarily on 62 ± 3 million year cycles. Image File history File links Circle-question. ...


It is difficult to evaluate the validity of these claims except through reduction to statistical arguments regarding how plausible or implausible it is for the observed data to exhibit a particular pattern, as the causes of most extinction events are still too uncertain to attribute to them any specific cause let alone a recurring one. Much early work in this area also suffered from poor knowledge of the geological time scale (errors > 10 million years at times), though the time scale now available (uncertainties all < 4 million years) should be adequate for studying these processes. // For other uses, see time scale. ...


While the statistics alone have been judged as sufficiently compelling to warrant publication, it is important to consider processes that might be responsible for a cyclic pattern of extinctions and future work may focus on trying to find evidence of such processes.


One theory, for which no real evidence exists, suggests that the extinction cycle could be caused by the orbit of a hypothetical companion star dubbed Nemesis that periodically disturbs the Oort cloud, sending storms of large asteroids and comets towards the Solar System. Another similar theory suggests that the Solar System's oscillations through the plane of the galaxy results in periods of comet showers. Other theories suggest geological instabilities that might allow heat to periodically build up deep in the Earth, which is then released through mantle plumes, periods of major volcanism and active plate tectonics. Artists impression of a binary system consisting of a black hole, with an accretion disc around it, and a main sequence star. ... Nemesis is a hypothetical red dwarf star or brown dwarf, orbiting the Sun at a distance of about 50,000 to 100,000 AU, somewhat beyond the Oort cloud. ... This image is an artists rendering of the Oort cloud and the Kuiper Belt. ... 253 Mathilde, a C-type asteroid. ... Comet Hale-Bopp Comet West For other uses, see Comet (disambiguation). ... Major features of the Solar System (not to scale; from left to right): Pluto, Neptune, Uranus, Saturn, Jupiter, the asteroid belt, the Sun, Mercury, Venus, Earth and its Moon, and Mars. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 17,000 parsecs in diameter and approximately 20 million parsecs distant. ... A lava lamp illustrates the basic concept of a mantle plume. ...


If any of these theories are correct, then it is worth noting that both Raup and Sepkoski and Rohde & Muller predict another naturally caused mass extinction event within the next 10 million years.


Controversy

In 2005, Andrew Smith and Alistair McGowan of the Natural History Museum suggested that the apparent variations in marine biodiversity may actually be caused by changes in the quantity of rock available for sampling from different time periods.[25] The diversity of the marine life appears to be proportional to the amount of rock available for study. However, statistical analysis shows that only half of the apparent diversity modification can be attributed to this effect. For other similarly-named museums see Museum of Natural History. ...


ELE in movies

For other films with this name, see Armageddon (disambiguation). ... Deep Impact is a 1998 disaster film/science fiction film released by Paramount Pictures and DreamWorks Pictures. ... It has been suggested that Operation Dark Storm be merged into this article or section. ... The Day After Tomorrow is a 2004 apocalyptic science-fiction film that depicts catastrophic effects of global warming and boasts high-end special effects, bending the lines between science, reality, and science fiction. ... The Day After is an American television movie which aired on November 20, 1983 on the ABC Television Network. ...

See also

Background extinction rate, also known as ‘normal extinction rate’, refers to the standard rate of extinction in earths geological and biological history before humans became a primary contributor to extinctions. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the hypocenter. ... In paleontology, an Elvis taxon (plural taxa) is a taxon which has been misidentified as having re-emerged in the fossil record after a period of extinction, but is not actually a descendant of the original taxon, instead having developed a similar morphology through convergent evolution. ... The Siberian Tiger, a subspecies of tiger. ... The takahe is an example of a Lazarus taxon. ... Near-Earth asteroids (NEAs) are asteroids whose orbits are close to Earths orbit. ... An Outside Context Problem or an OCP is any problem outside a given organisation or societys experience, with an immediate, ubiquitous and lasting impact upon an entire culture or civilisation. ... Map of countries by population density (See List of countries by population density. ... Rare species is an organism which is very uncommon or scarce. ... This article or section contains a plot summary that may be overly long, confusing, or ambiguous. ... The Signor-Lipps effect is a paleontological effect describing the fossil records reflection of a extinction event, such as the proposed impact event that caused the extinction of the dinosaurs. ... One computer simulation of conditions during the Snowball Earth period. ... The timeline of extinctions is an historical account of species that have gone extinct during the time that modern humans have occupied the earth. ...

References

  1. ^ Bambach, R.K.; A.H. Knoll & S.C. Wang (December 2004), "Origination, extinction, and mass depletions of marine diversity", Paleobiology 30 (4): 522–542
  2. ^ Raup, D. & Sepkoski, J. (1982). "Mass extinctions in the marine fossil record". Science 215: 1501–1503. 
  3. ^ Raup, D. & Sepkoski, J. (1982). "Mass extinctions in the marine fossil record". Science 215: 1501–1503. 
  4. ^ Eldredge, Niles (June 2001). The Sixth Extinction. ActionBioscience.org. Retrieved on 2006-03-17.
  5. ^ Regan, H.M.; R Lupia & A.N. Drinnan et al. (2001), "The Currency and Tempo of Extinction", The American Naturalist 157: 1–10, University of Chicago Press
  6. ^ Benton, M.J. (2004). "6. Reptiles Of The Triassic", Vertebrate Palaeontology. Blackwell. 
  7. ^ Jablonski, D. (2002). "Survival without recovery after mass extinctions". PNAS 99 (12): 8139-8144. 
  8. ^ MacLeod, Norman (6 Jan 2001). Extinction!.
  9. ^ Martin, R.E. (1995). "Cyclic and secular variation in microfossil biomineralization: clues to the biogeochemical evolution of Phanerozoic oceans". Global and Planetary Change 11 (1). 
  10. ^ Martin, R.E. (1996). "Secular increase in nutrient levels through the Phanerozoic: Implications for productivity, biomass, and diversity of the marine biosphere". Palaios 11: 209-219. 
  11. ^ Marshall, C.R. (1996). "Sudden and Gradual Molluscan Extinctions in the Latest Cretaceous of Western European Tethys". Science 274: 1360-1363. 
  12. ^ Arens, N.C. and West, I.D. (2006). "Press/Pulse: A General Theory of Mass Extinction?"" 'GSA Conference paper' Abstract
  13. ^ MacLeod, N (6 Jan 2001). Extinction!.
  14. ^ Courtillot, V., Jaeger, J-J., Yang, Z., Féraud, G., Hofmann, C. (1996). "The influence of continental flood basalts on mass extinctions: where do we stand?" in Ryder, G., Fastovsky, D., and Gartner, S, eds. "The Cretaceous-Tertiary event and other catastrophes in earth history". The Geological Society of America, Special Paper 307, 513-525.
  15. ^ Hallam, A. (1992). "Phanerozoic sea-level changes". New York; Columbia University Press.
  16. ^ Grieve, R., Rupert, J., Smith, J., Therriault, A. (1996). "The record of terrestrial impact cratering". GSA Today 5: 193-195
  17. ^ The earliest known flood basalt event is the one which produced the Siberian Traps and is associated with the end-Permian extinction.
  18. ^ a b Some of the extinctions associated with flood basalts and sea-level falls were significantly smaller than the "major" extinctions, but still much greater than the background extinction level.
  19. ^ Wignall, P.B. (2001), "Large igneous provinces and mass extinctions", Earth-Science Reviews vol. 53 issues 1-2 pp 1-33
  20. ^ Hecht, J (26 March 2002). Methane prime suspect for greatest mass extinction. New Scientist.
  21. ^ Berner, R.A., and Ward, P.D. (2004). "Positive Reinforcement, H2S, and the Permo-Triassic Extinction: Comment and Reply" describes possible positive feedback loops in the catastrophic release of hydrogen sulphide proposed by Kump, Pavlov and Arthur (2005).
  22. ^ Kump, L.R., Pavlov, A., and Arthur, M.A. (2005). "Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia". Geology v. 33, p.397–400. Abstract. Summarised by Ward (2006).
  23. ^ Ward, P.D. (2006). "Impact from the Deep". Scientific American October 2006.
  24. ^ {{Citation | last=Wilde | first=P | last2=Berry | first2=W.B.N. | title=Destabilization of the oceanic density structure and its significance to marine "extinction" events | journal=Palaeogeography, Palaeoclimatology, Palaeaecology | volume=48 | pages=143-162 | year=1984 | url=http://www.marscigrp.org/ppp84.html}
  25. ^ Smith, A.; A. McGowan (2005). "Cyclicity in the fossil record mirrors rock outcrop area". Biology Letters 1 (4): 443–445. DOI:10.1098/rsbl.2005.0345. 

For the Manfred Mann album, see 2006 (album). ... is the 76th day of the year (77th in leap years) in the Gregorian calendar. ... The Siberian Traps (Russian: ) form a large igneous province in Siberia. ... The Permian-Triassic extinction event, labeled End P here, is the most significant extinction event in this plot for marine fossiliferous genera. ... Positive feedback is a feedback system in which the system responds to the perturbation in the same direction as the perturbation (It is sometimes referred to as cumulative causation). ... For other meaning link to H2S radar. ... There are very few or no other articles that link to this one. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

Further reading

  • Cowen, R. (1999). "The History of Life". Blackwell Science. The chapter about extinctions is reproduced at [1]
  • Richard Leakey and Roger Lewin, 1996, The Sixth Extinction : Patterns of Life and the Future of Humankind, Anchor, ISBN 0-385-46809-1. Excerpt from this book: The Sixth Extinction
  • Wilson, E.O., 2002, The Future of Life, Vintage (pb), ISBN 0-679-76811-4
  • Raup, D., and J. Sepkoski (1986). "Periodic extinction of families and genera". Science 231 (4740): 833-836. DOI:10.1126/science.11542060. 
  • Rohde, R.A. & Muller, R.A. (2005). "Cycles in fossil diversity". Nature 434 (7030): 209-210. DOI:10.1038/nature03339. 
  • The Current Mass Extinction Event
  • Nemesis — Raup and Sepkoski
  • Richard A. Muller, 1988, Nemesis, Weidenfeld & Nicolson, ISBN 1-55584-173-2
  • Robert J. Sawyer, 2000, Calculating God, TOR, ISBN 0-812-58035-4
  • Ward Peter D., (2000) Rivers In Time: The Search for Clues to Earth's Mass Extinctions

In 1977, Leaky sat next to the rare Half Monkey Half Man, who took a bite out of him, and made Leaky cry. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Richard Muller Richard A. Muller (January 6, 1944 -) of San Francisco, California, USA, is a physicist who works at the University of California, Berkeley and Lawrence Berkeley National Laboratory. ... Robert J. Sawyer is a Canadian science fiction writer, dubbed the dean of Canadian science fiction by the Ottawa Citizen in 1999. ...

External links


  Results from FactBites:
 
Bagheera: An Endangered Species and Endangered Animal Online Education Resource (935 words)
Extinctions are a natural part of evolutionary processes, but through most of the history of life on Earth, biological diversity has been increasing.
Extinctions in the ancient past frequently are described in terms of whole groups of related species, such as a genus or a family.
The extinction case studies represent a broad geographical and temporal range of extinctions that were caused by humans or are believed to have been caused by humans.
  More results at FactBites »

 
 

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