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For the Big Finish Productions audio play, see The Extinction Event. The Extinction Event is a Big Finish Productions audio drama featuring Lisa Bowerman as Bernice Summerfield, a character from
For Busta Rhymes album, see E.L.E. (Extinction Level Event): The Final World Front. ELE (Extinction Level Event The Final World Front is a hip hop album by Busta Rhymes, released on December 8, 1998 (see

An extinction event (also known as: mass extinction; extinction-level event, ELE) is a sharp decrease in the number of species in a relatively short period of time. In Biology, a species is one of the basic units of Biological classification and a Taxonomic rank. Mass extinctions affect most major taxonomic groups present at the time — birds, mammals, reptiles, amphibians, fish, invertebrates and other simpler life forms. Taxonomy is the practice and science of classification The word comes from the Greek, taxis (meaning 'order' 'arrangement' and, nomos Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate They may be caused by one or both of:

Over 99% of species that ever lived are now extinct, but extinction occurs at an uneven rate. 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. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. In Biology and Ecology, extinction is the cessation of existence of a Species or group of taxa. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Taxonomy, sometimes alpha taxonomy, is the Science of finding describing and categorising Organisms thus giving rise to taxonomic groups or taxa In Biological classification, family ( Latin An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes [2] Marine fossils are mostly used to measure extinction rates because they are more plentiful and cover a longer time span than fossils of land organisms.

Millions of years ago
 
Apparent extinction intensity, i. The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial The Late Devonian extinction was one of five major Extinction events in the history of the Earth's Biota. e. the fraction of genera going extinct at any given time, as reconstructed from the fossil record. A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. (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. The Holocene extinction event is the widespread ongoing Mass extinction of Species during the modern Holocene epoch. The most recent, the Cretaceous–Tertiary extinction event, occurred 65 million years ago, and has attracted more attention than all others because it killed the dinosaurs. The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically In the past 550 million years there have been five major events when over 50% of animal species died. There probably were mass extinctions in the Archean and Proterozoic Eons, but before the Phanerozoic there were no animals with hard body parts to leave a significant fossil record. The Proterozoic (ˌproʊtərəˈzoʊɪk is a geological eon representing a period before the first abundant complex life on Earth. The Phanerozoic (occasionally Phanaerozoic) Eon is the current eon in the Geologic timescale, and the one during which abundant animal life has existed

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 from the threshold chosen for describing an extinction event as "major", and the data chosen to measure 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. J John Sepkoski Jr. ( July 26, 1948 - May 1, 1999) was a University of Chicago Paleontologist. David M Raup is a University of Chicago Paleontologist. Raup studied the Fossil record and the diversity of life on Earth. The Late Devonian extinction was one of five major Extinction events in the history of the Earth's Biota. The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically [2]

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.

Timeline of mass extinctions on Earth within the past 500 million years
  1. Present day — the Holocene extinction event. The Holocene extinction event is the widespread ongoing Mass extinction of Species during the modern Holocene epoch. 70% of biologists view the present era as part of a mass extinction event, possibly one of the fastest ever, according to a 1998 survey by the American Museum of Natural History. The American Museum of Natural History ( AMNH) located on the Upper West Side, Manhattan, New York, USA is one of the largest and most Some, such as E. O. Wilson of Harvard University, predict that humanity's destruction of the biosphere could cause the extinction of one-half of all species in the next 100 years. Edward Osborne Wilson (born June 10, 1929) is an American biologist researcher ( Sociobiology, Biodiversity) theorist ( The biosphere is the broadest level of ecological study the global sum of all Ecosystems. 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 IUCN Red List of Threatened Species (also known as the IUCN Red List or Red Data List) created in 1963 is the world's most comprehensive inventory of the global The extinction of many megafauna near the end of the most recent ice age is also sometimes considered part of the Holocene extinction event. Megafauna are species of large Animals ( Greek μεγας large + modern Latin fauna animal An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets The Holocene is a Geological epoch which began approximately 10000 years ago (about 8000 BC [3] Some paleontologists, however, question whether the available data support a comparison with mass extinctions in the past. Palaeontology redirects here For the Scientific journal, see Palaeontology (journal. [4]
  2. 65 MY ago — at the Cretaceous-Paleogene transition (the K/T or Cretaceous–Tertiary extinction event) about 50% of all species became extinct. The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of The Paleogene (alternatively Palaeogene) is a geologic period and system that began 65 The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically It has great significance for humans because it ended the reign of dinosaurs and opened the way for mammals to become the dominant land vertebrates. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands In the seas it reduced the percentage of sessile animals to about 33%. Sessile is a term in Biology with two distinct meanings In botany and medicine In Botany, sessile means "without a stalk The K/T extinction was rather uneven — some groups of organisms became extinct, some suffered heavy losses and some appear to have been only minimally affected.
  3. 200 MY 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. The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago The Jurassic is a geologic period and system that extends from about Ma (million years ago to  Ma that is from the end of the Triassic to the beginning Archosaurs ( Greek for 'ruling lizards' are a group of Diapsid Reptiles represented by Modern birds and Crocodilians This group also Therapsids are an order of Synapsids (Class Synapsida Traditionally synapsids were referred to as Reptiles and were known as Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and
  4. 251 MY 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 Permian is a geologic period and system that extends from 299 The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic The "Great Dying" had enormous evolutionary significance: on land it ended the dominance of 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%. Synapsids ('fused arch' also known as theropsids ('beast face' are a class of Animals that includes Mammals and everything closer to mammals than Archosaurs ( Greek for 'ruling lizards' are a group of Diapsid Reptiles represented by Modern birds and Crocodilians This group also Sessile is a term in Biology with two distinct meanings In botany and medicine In Botany, sessile means "without a stalk The whole late Permian was a difficult time for at least marine life — even before the "Great Dying", there was level of extinction large enough to be included in the "Big Five".
  5. 360 MY ago — near the Devonian-Carboniferous transition (the Late Devonian extinction) a prolonged series of extinctions eliminated about 70% of all species. The Devonian is a geologic period and system of the Paleozoic era spanning from to  million years ago. The Carboniferous is a geologic period and system that extends from the end of the Devonian period about 359 The Late Devonian extinction was one of five major Extinction events in the history of the Earth's Biota. This was not a sudden event — it lasted perhaps as long as 20 MY, and there is evidence for a series of extinction pulses within this period.
  6. 444 MY ago — at the Ordovician-Silurian transition two Ordovician-Silurian extinction events occurred, and together 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. The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 The Silurian is a geologic period and system that extends from the end of the Ordovician period about 443 A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic
  7. 488 million years (MY) 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. The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 The Cambrian–Ordovician extinction event occurred approximately 488 million years ago Brachiopods (from Latin brachium, arm + New Latin -poda, foot are a small phylum of Benthic Invertebrates Also Conodonts are extinct chordates resembling eels classified in the class Conodonta. Trilobites ("three-lobes" are extinct Arthropods that form the class Trilobita.

It has been suggested that the apparent variations in marine biodiversity may actually be an artefact, with abundance estimates directly related to quantity of rock available for sampling from different time periods. [5] However, statistical analysis shows that this can only account for 50% of the observed pattern, and other evidence (such as fungal spikes) provides reassurance that most widely accepted extinction events are indeed real. A quantification of the rock exposure of Western Europe does indicate that many of the minor events for which a biological explanation has been sought are most readily explained by sampling bias. [6]

Evolutionary importance

Mass extinctions have sometimes accelerated the evolution of life on earth. Life on Earth A Natural History by David Attenborough is a groundbreaking television Natural history series made by the BBC in association with 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. [7][8]

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. Mammaliaformes ("mammal-shaped" is a Clade that contains the Mammals and their closest extinct relatives Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands The end-Cretaceous mass extinction removed the non-avian dinosaurs and made it possible for mammals to expand into the large terrestrial vertebrate niches. The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically

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, and these are often referred to as "Dead Clades Walking". The phrase Dead Clade Walking refers to the fact that some clades (groups of organisms which survive Mass extinctions either become extinct a few million years after [9] So analysing extinctions in terms of "what died and what survived" often fails to tell the full story.

Apparent decreasing frequency

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

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. Statistics is a mathematical science pertaining to the collection analysis interpretation or explanation and presentation of Data. 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.

Both of these phenomena could be explained in one or more ways:[10]

Causes

There is still debate about the causes of all mass extinctions before the Holocene. The Holocene extinction event is the widespread ongoing Mass extinction of Species during the modern Holocene epoch.

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.

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. The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically [13]

Arens and West (2006) proposed a "press / pulse" model in which mass extinctions generally require two types of cause: long-term pressure on the eco-system ("press") and a sudden catastrophe ("pulse") towards the end of the period of pressure. [14] 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 Phanaerozoic) Eon is the current eon in the Geologic timescale, and the one during which abundant animal life has existed

Most widely-supported explanations

Macleod (2001)[15] 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),[16] Hallam (1992)[17] and Grieve et al (1996):[18]

The most commonly-suggested causes of mass extinctions are listed below

Flood basalt events

The formation of large igneous provinces by flood basalt events could have:

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. The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial

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. Orogeny (Greek for "mountain generating" is the process of natural Mountain building and may be studied as a tectonic structural event as a geographical event and 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. Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere

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. The Late Devonian extinction was one of five major Extinction events in the history of the Earth's Biota. The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically

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. Food chains, also called food networks and/or trophic networks, describe the feeding relationships between species within an Ecosystem. Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas If it hits 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. Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 Acid rain is Rain or any other form of precipitation that is unusually Acidic It has harmful effects on plants aquatic animals and infastructure Some scientists have suggested that impacts could also have caused megatsunamis and / or global forest fires, but these ideas are now regarded as exaggerations. Mega-tsunami (also known as iminami or "wave of purification" is an informal term to indicate a Tsunami that has initial Wave heights that are A wildfire, also known as a wildland fire, forest fire, brush fire, vegetation fire, grass fire, Peat fire,

Only the Cretaceous–Tertiary extinction event is associated with strong evidence of such an impact, but that impact is easily the largest for which there is strong evidence. The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically

Sustained and significant global cooling

Sustained global cooling 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. A polar circle is either the Arctic Circle or the Antarctic Circle. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the The Tropics are centered on the Equator and limited in Latitude by the Tropic of Cancer in the northern hemisphere at approximately 23°26' (23 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. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets

It has been suggested that global cooling caused or contributed to the End-Ordovician, Permian-Triassic, Late Devonian extinctions, and possibly others. The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial The Late Devonian extinction was one of five major Extinction events in the history of the Earth's Biota. Sustained global cooling is distinguished from the temporary climatic effects of flood basalt events or impacts.

Sustained and significant 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. The Tropics are centered on the Equator and limited in Latitude by the Tropic of Cancer in the northern hemisphere at approximately 23°26' (23 A polar circle is either the Arctic Circle or the Antarctic Circle. The Earth 's Water is always in movement and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on above 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. The Paleocene /Eocene boundary, was marked by the most rapid and significant climatic disturbance of the Cenozoic Era. It has also been suggested to have caused the Triassic-Jurassic extinction event, during which 20% of all marine families went extinct.

Global warming as a cause of mass extinction is supported by a 2007 study by the Royal Society. [3]

Clathrate gun hypothesis

Main article: Clathrate Gun Hypothesis

Clathrates are composites in which a lattice of one substance forms a cage round another. The clathrate gun hypothesis is the popular name given to the hypothesis that rises in sea temperatures (and/or falls in sea level can trigger the sudden release of Methane A clathrate or clathrate compound or cage compound is a Chemical substance consisting of a lattice of one type of molecule trapping Methane clathrates (in which water molecules are the cage) form on continental shelves. Methane clathrate, also called methane hydrate or methane ice, is a solid form of water that contains a large amount of Methane within its Crystal The continental shelf is the extended perimeter of each Continent and associated Coastal plain, which is covered during interglacial periods such 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. Global warming is the increase in the average measured temperature of the An earthquake is the result of a sudden release of energy in the Earth 's crust that creates Seismic waves Earthquakes are recorded with a Seismometer 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 Greenhouse effect refers to the change in the Thermal equilibrium temperature of a planet or moon by the presence of an Atmosphere containing gas that absorbs

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. Isotope analysis is the identification of Isotopic signature, the distribution of certain Stable isotopes and chemical elements within chemical compounds [22]

It has been suggested that "clathrate gun" methane eruptions were involved in the end-Permian extinction ("the Great Dying") and in the Paleocene-Eocene Thermal Maximum, which was associated with one of the smaller mass extinctions. The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial The Paleocene /Eocene boundary, was marked by the most rapid and significant climatic disturbance of the Cenozoic Era.

Anoxic events

Anoxic events are situations in which the upper and even the middle layers of the ocean become deficient or totally lacking in oxygen. Oceanic anoxic events or Anoxic events occur when the Earth 's Oceans become completely depleted of oxygen (O2 below the surface levels 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. The Late Devonian extinction was one of five major Extinction events in the history of the Earth's Biota. The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial 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.

Hydrogen sulfide emissions from the seas

Kump, Pavlov and Arthur (2005) have proposed that during the Permian-Triassic extinction event 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. The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Sulfate-reducing bacteria comprise several groups of bacteria that use Sulfate as an oxidizing agent reducing it to Sulfide. Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays [23][24][25]

Oceanic overturn

Oceanic overturn 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. The term thermohaline circulation (THC refers to the part of the large-scale ocean circulation that is thought to be driven by global density gradients created by surface heat and 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. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. [26]

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. The Late Devonian extinction was one of five major Extinction events in the history of the Earth's Biota. The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial

A nearby nova, supernova or gamma ray burst

A nearby gamma ray burst (fewer than 6000 light years away) could sufficiently irradiate the surface of Earth to kill organisms living there and destroy the ozone layer in the process. Gamma-ray bursts ( GRB s are the most luminous electromagnetic events occurring in the Universe since the Big Bang. A light-year or light year (symbol ly) is a unit of Length, equal to just under ten trillion Kilometres As defined by The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 From statistical arguments, approximately 1 gamma ray burst would be expected to occur close 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. A supernova (plural supernovae or supernovas) is a stellar Explosion.

It has been suggested that a supernova or gamma ray burst caused the End-Ordovician extinction.

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). An ice age is a period of long-term reduction in the Temperature of the Earth 's surface and atmosphere resulting in an expansion of continental Ice sheets Marsupials are an Infraclass of Mammals characterized by a distinctive pouch (called the marsupium) in which females carry their young through 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. The continental shelf is the extended perimeter of each Continent and associated Coastal plain, which is covered during interglacial periods such

It is widely thought that the creation of the super-continent Pangaea contributed to the End-Permian mass extinction. Pangaea, Pangæa or Pangea (pænˈdʒiːə from παν pan, meaning entire, and Γαῖα Gaea, meaning Earth in The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial 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.

Plate tectonics

Plate tectonics is the mechanism which drives many of the possible causes of mass extinctions, especially volcanism and continental drift. Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere So it is implicated in many extinctions, but in each case it is necessary to specify which manifestations of plate tectonics were involved.

Other hypotheses

Many other hypotheses have been proposed, such as the spread of a new disease or simple out-competition following an especially successful biological innovation. A disease is an abnormal condition of an organism that impairs bodily functions and can be deadly 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.

Postulated extinction cycles

It has been suggested by several sources that biodiversity and/or extinction events may be influenced by cyclic processes. The best-known hypothesis of extinction events by a cyclic process is the 26M to 30M year cycle in extinctions proposed by Raup and Sepkoski (1986). [27] More recently, Rohde and Muller (2005) have suggested that biodiversity fluctuates primarily on 62 ± 3 million year cycles. [28]

It is difficult to evaluate the validity of such claims except through reduction to statistical arguments about 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 the poor accuracy of geological dating, where errors often exceed 10M years. However, improvements in radiometric dating have reduced the scale of uncertainty to at most 4M years — theoretically adequate for studying these processes. Radiometric dating (often called radioactive dating) is a technique used to date materials usually based on a comparison between the observed abundance of a naturally occurring

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.

Hypothetical companion star to the sun

The physicist Richard A. Muller has produced a number of speculative hypotheses for the regularity of mass extinctions. Richard A Muller of San Francisco California, US, is a Physicist who works at the University of California Berkeley and Lawrence Berkeley One is 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. A binary star is a Star system consisting of two Stars orbiting around their Center of mass. Nemesis is a hypothetical Red dwarf star or Brown dwarf, orbiting the Sun at a distance of about 50000 to 100000 AU, somewhat The Oort cloud ( ort alternatively the Öpik-Oort Cloud) is a hypothetical spherical cloud of Comets believed to lie roughly 50 000 AU, Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — The Solar System consists of the Sun and those celestial objects bound to it by Gravity. [29]

Galactic plane oscillations

Muller has also speculated the periodicity of mass extinctions may be related to the solar system's oscillation through the plane of our Milky Way galaxy as it rotates around the galactic centre, with a number of possible hypothesized effects including gravitationally-induced comet showers or periods of intense radiation as the solar system hits the galactic shock wave. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply [30][31]

Passage through galactic spiral arms

It has also been suggested that extinction events correlate to the passage of the solar system through the spiral arms of the Milky Way. The earth passes through all four arms every 700 million years, and there is some evidence to suggest a cyclicity of extraterrestrial activity back to 2 billion years ago. [32]

Geological instabilities

Other hypotheses are that geological instabilities 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. A mantle plume is an upwelling of abnormally hot rock within the Earth's mantle. Plate tectonics and hotspots Divergent plate boundaries At the Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere

Impending Mass Extinction

Main article: Holocene extinction event

Paleontologist Peter Ward offers evidence in his April 2007 book, Under a Green Sky, that all but one of the major extinction events in history have been brought on by climate change — the same global warming that occurs today. The Holocene extinction event is the widespread ongoing Mass extinction of Species during the modern Holocene epoch. Peter Douglas Ward is a Paleontologist and professor of Biology and of Earth and Space Sciences at the University of Washington, Seattle as well as an author of popular Reviewer Doug Brown goes further, stating [33]. Scientists at the Universities of York and Leeds also warn that the [34] fossil record supports evidence of impending mass extinction, according to a ScienceDaily release, Oct. Dan Hogan Editoreditor@sciencedailycom Michele Hogan Sales Managersales@sciencedaily 24, 2007.

See also

References

  1. ^ Bambach, R. Background extinction rate, also known as ‘normal extinction rate’ refers to the standard rate of Extinction in earth’s geological and biological history before humans A doomsday event is a specific occurrence which has an exceptionally destructive effect on the human race In Paleontology, an Elvis taxon (plural Elvis taxa) is a Taxon which has been misidentified as having re-emerged in the Fossil record after a An endangered species is a population of an organism which is at risk of becoming Extinct because it is either few in numbers or threatened by changing environmental or predation In Paleontology, a Lazarus taxon (plural taxa) is a Taxon that disappears from one or more periods of the Fossil record, only to appear The term Middle Miocene disruption alternatively the Middle Miocene extinction or Middle Miocene extinction peak refers to a wave of extinctions of terrestrial Near-Earth asteroids (NEAs are Asteroids whose Orbits are close to Earth 's orbit Overpopulation refers to a condition where an Organism 's numbers exceed the Carrying capacity of its Habitat. A rare species is an Organism which is very uncommon or scarce The Revenge of Gaia Why the Earth is Fighting Back - and How we Can Still Save Humanity (2006 is a book by James Lovelock. The Signor-Lipps effect is a Paleontological principle proposed by Philip W The Snowball Earth Hypothesis as it was originally proposed]] Evidence The Snowball Earth hypothesis was originally devised to explain the apparent presence of The timeline of extinctions is an historical account of species that have gone extinct during the time that modern humans have occupied the earth Deep Impact is a 1998 sci-fi - drama Disaster film released by Paramount Pictures and DreamWorks SKG in the K. ; Knoll, A. H. & Wang, S. C. (December 2004), “Origination, extinction, and mass depletions of marine diversity”, Paleobiology 30 (4): 522–542, <http://findarticles.com/p/articles/mi_qa4067/is_200410/ai_n9458414/pg_1> 
  2. ^ a b Raup, D. & Sepkoski, J. (1982). "Mass extinctions in the marine fossil record". Science 215: 1501–1503. doi:10.1126/science.215.4539.1501. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  3. ^ Eldredge, Niles (June 2001). The Sixth Extinction. ActionBioscience. org. Retrieved on 2006-03-17. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 45 BC - In his last victory Julius Caesar defeats the Pompeian forces of Titus Labienus and Pompey the Younger
  4. ^ Regan, H. M. ; Lupia, R; Drinnan, A. N. & Burgman, M. A. (2001), “The Currency and Tempo of Extinction”, The American Naturalist (University of Chicago Press) 157: 1–10, <http://www.journals.uchicago.edu/cgi-bin/resolve?id=doi:10.1086/317005&erFrom=-553768327590922063Guest> 
  5. ^ Smith, A. ; A. McGowan (2005). "Cyclicity in the fossil record mirrors rock outcrop area". Biology Letters 1 (4): 443–445. Biology Letters ( is a journal covering a wide spectrum of the biological sciences published both in print and online doi:10.1098/rsbl.2005.0345. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  6. ^ ANDREW B. SMITH, ALISTAIR J. McGOWAN (July 2007). "THE SHAPE OF THE PHANEROZOIC MARINE PALAEODIVERSITY CURVE: HOW MUCH CAN BE PREDICTED FROM THE SEDIMENTARY ROCK RECORD OF WESTERN EUROPE?" 50: 765-774. doi:10.1111/j.1475-4983.2007.00693.x. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  7. ^ Benton, M. J. (2004). "6. Reptiles Of The Triassic", Vertebrate Palaeontology. Blackwell.  
  8. ^ Van Valkenburgh, B. (1999). "Major patterns in the history of xarnivorous mammals". Annual Review of Earth and Planetary Sciences 26: 463-493. doi:10.1146/annurev.earth.27.1.463. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  9. ^ Jablonski, D. (2002). "Survival without recovery after mass extinctions". PNAS 99 (12): 8139-8144. doi:10.1073/pnas.102163299. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  10. ^ MacLeod, Norman (6 Jan 2001). Extinction!.
  11. ^ 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).  
  12. ^ 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.  
  13. ^ Marshall, C. R. (1996). "Sudden and Gradual Molluscan Extinctions in the Latest Cretaceous of Western European Tethys". Science 274: 1360-1363. doi:10.1126/science.274.5291.1360. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  14. ^ Arens, N. C. and West, I. D. (2006). "Press/Pulse: A General Theory of Mass Extinction?"" 'GSA Conference paper' Abstract
  15. ^ MacLeod, N (6 Jan 2001). Extinction!.
  16. ^ 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.
  17. ^ Hallam, A. (1992). "Phanerozoic sea-level changes". New York; Columbia University Press.
  18. ^ Grieve, R. , Rupert, J. , Smith, J. , Therriault, A. (1996). "The record of terrestrial impact cratering". GSA Today 5: 193-195
  19. ^ The earliest known flood basalt event is the one which produced the Siberian Traps and is associated with the end-Permian extinction. The Siberian Traps (Сибирские траппы form a Large igneous province in Siberia. The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial
  20. ^ 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.
  21. ^ Wignall, P. B. (2001), "Large igneous provinces and mass extinctions", Earth-Science Reviews vol. 53 issues 1-2 pp 1-33
  22. ^ Hecht, J (26 March 2002). Methane prime suspect for greatest mass extinction. New Scientist.
  23. ^ 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 sulfide proposed by Kump, Pavlov and Arthur (2005). Positive feedback, sometimes referred to as "cumulative causation" is a Feedback loop system in which the system responds to perturbation in the same direction Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S.
  24. ^ 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).
  25. ^ Ward, P. D. (2006). "Impact from the Deep". Scientific American October 2006.
  26. ^ Wilde, P & Berry, W. B. N. (1984), “Destabilization of the oceanic density structure and its significance to marine "extinction" events”, Palaeogeography, Palaeoclimatology, Palaeaecology 48: 143-162, <http://www.marscigrp.org/ppp84.html> 
  27. ^ Raup, D. M. ; Sepkoski, J. J. (1984-02-01). Year 1984 ( MCMLXXXIV) was a Leap year starting on Sunday (link displays the 1984 Gregorian calendar) Events 1327 - Teenaged Edward III is crowned King of England, but the country is ruled by his mother Queen "Periodicity of Extinctions in the Geologic Past". Proceedings of the National Academy of Sciences 81 (3): 801-805. doi:10.1073/pnas.81.3.801. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  28. ^ Rohde, R. A. ; Muller, R. A. (2005). "Cycles in fossil diversity". Nature 434 (7030): 208-10. doi:10.1038/nature03339. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  29. ^ R. A. Muller. Nemesis. Muller. lbl. gov. Retrieved on 2007-05-19. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1535 - French explorer Jacques Cartier sets sail on his second voyage to North America with three ships 110 men and
  30. ^ David Perlman (March 10, 2005). Mass extinction comes every 62 million years, UC physicists discover. Retrieved on 2007-07-09. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 455 - Roman military commander Avitus is proclaimed Emperor of the Western Roman Empire.
  31. ^ Christopher Mims (July 26, 2007). In 12 million years, we're dead. Retrieved on 2007-07-09. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 455 - Roman military commander Avitus is proclaimed Emperor of the Western Roman Empire.
  32. ^ Michael Gillmana ; Hilary Erenlera (2008). "The galactic cycle of extinction". Astrobiology. doi:10.1017/S1473550408004047. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  33. ^ [1] "This Is How The World Ends"
  34. ^ [2]

Further reading

External links

The Cloudinids, early Metazoan family containing the Genus Cloudina, lived in the late Ediacaran period and The Lau event was the last of three relatively minor Mass extinctions during the Silurian period having a major effect on the Conodont fauna (but barely The term Toarcian turnover alternatively the Toarcian extinction the Pliensbachian-Toarcian extinction or the Early Jurassic extinction refers to the The Aptian extinction was an Extinction event of the early Cretaceous Period. The term Middle Miocene disruption alternatively the Middle Miocene extinction or Middle Miocene extinction peak refers to a wave of extinctions of terrestrial The Cambrian–Ordovician extinction event occurred approximately 488 million years ago The Late Devonian extinction was one of five major Extinction events in the history of the Earth's Biota. The Permian–Triassic (P–Tr extinction event, informally known as the Great Dying, was an Extinction event that occurred, and 70 percent of terrestrial The Cretaceous–Tertiary extinction event, which occurred approximately ( Ma) was a large-scale mass extinction of animal and plant species in a geologically The Holocene extinction event is the widespread ongoing Mass extinction of Species during the modern Holocene epoch. The Ediacaran Period (ˌiːdiˈækərən named after the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with The Ordovician is a geologic period and system, the second of six of the Paleozoic era, and covers the time between 488 The Silurian is a geologic period and system that extends from the end of the Ordovician period about 443 The Devonian is a geologic period and system of the Paleozoic era spanning from to  million years ago. The Carboniferous is a geologic period and system that extends from the end of the Devonian period about 359 The Permian is a geologic period and system that extends from 299 The Triassic is a geologic period and system that extends from about 251 to 199 Ma (million years ago The Jurassic is a geologic period and system that extends from about Ma (million years ago to  Ma that is from the end of the Triassic to the beginning The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of The Paleogene (alternatively Palaeogene) is a geologic period and system that began 65 The Neogene is a geologic period and system starting 2303 ± 0
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