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Skeleton of Palaeoloxodon namadicus, an extinct elephant species
Skeleton of various extinct dinosaurs; some other dinosaur lineages still flourish in the form of birds
CitationClass=book }}</ref>

In biology and ecology, extinction is the end of an organism or of a group of organisms (taxon), normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "reappears" (typically in the fossil record) after a period of apparent absence.

The age of the Earth is about 4.54 billion years old.<ref name="USGS1997">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }} </ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago,<ref name="Origin1">Schopf, JW, Kudryavtsev, AB, Czaja, AD, and Tripathi, AB. (2007). Evidence of Archean life: Stromatolites and microfossils. Precambrian Research 158:141–155.</ref><ref name="Origin2">Schopf, JW (2006). Fossil evidence of Archaean life. Philos Trans R Soc Lond B Biol Sci 29;361(1470) 869-85.</ref><ref name="RavenJohnson2002">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia.<ref name="AP-20131113">{{#invoke:citation/CS1|citation |CitationClass=news }}</ref><ref name="TG-20131113-JP">{{#invoke:citation/CS1|citation |CitationClass=news }}</ref><ref name="AST-20131108">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Earlier physical evidences of life include graphite, a biogenic substance, in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland,<ref name="NG-20131208">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> as well as, "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia.<ref name="AP-20151019">{{#invoke:citation/CS1|citation |CitationClass=news }}</ref><ref name="PNAS-20151014-pdf">{{#invoke:Citation/CS1|citation |CitationClass=journal }} Early edition, published online before print.</ref> According to one of the researchers, "If life arose relatively quickly on Earth ... then it could be common in the universe."<ref name="AP-20151019" />

More than 99 percent of all species, amounting to over five billion species,<ref name="Book-Biology">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> that ever lived on Earth are estimated to be extinct.<ref name="StearnsStearns2000">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref><ref name="NYT-20141108-MJN">{{#invoke:citation/CS1|citation |CitationClass=news }}</ref><ref name="Newman" /> Estimates on the number of Earth's current species range from 10 million to 14 million,<ref name="MillerSpoolman2012">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> of which about 1.2 million have been documented and over 86 percent have not yet been described.<ref name="PLoS-20110823">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>

Through evolution, species arise through the process of speciation—where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche—and species become extinct when they are no longer able to survive in changing conditions or against superior competition. The relationship between animals and their ecological niches has been firmly established.<ref name="SahneyBentonFerry2010LinksDiversityVertebrates">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> A typical species becomes extinct within 10 million years of its first appearance,<ref name="Newman">Newman, Mark. A model of mass extinction. 1997. Journal of Theoretical Biology 189: 235–252</ref> although some species, called living fossils, survive with virtually no morphological change for hundreds of millions of years.

Mass extinctions are relatively rare events; however, isolated extinctions are quite common. Only recently have extinctions been recorded and scientists have become alarmed at the current high rate of extinctions.<ref name="MSNBC">Species disappearing at an alarming rate, report says. MSNBC. Retrieved July 26, 2006.</ref> Most species that become extinct are never scientifically documented. Some scientists estimate that up to half of presently existing plant and animal species may become extinct by 2100.<ref name="Wilson">Wilson, E.O., The Future of Life (2002) (ISBN 0-679-76811-4). See also: Leakey, Richard, The Sixth Extinction : Patterns of Life and the Future of Humankind, ISBN 0-385-46809-1</ref>


Extinction sections
Intro   Definition    Causes    Mass extinctions    History of scientific understanding    Human attitudes and interests    See also   References   External links   

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Species::first    Extinct::title    Journal::genetic    Author::which    Pages::biology    Years::other

{{#invoke:redirect hatnote|redirect}} {{#invoke:Infobox|infobox}}

Skeleton of Palaeoloxodon namadicus, an extinct elephant species
Skeleton of various extinct dinosaurs; some other dinosaur lineages still flourish in the form of birds
CitationClass=book }}</ref>

In biology and ecology, extinction is the end of an organism or of a group of organisms (taxon), normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "reappears" (typically in the fossil record) after a period of apparent absence.

The age of the Earth is about 4.54 billion years old.<ref name="USGS1997">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }} </ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago,<ref name="Origin1">Schopf, JW, Kudryavtsev, AB, Czaja, AD, and Tripathi, AB. (2007). Evidence of Archean life: Stromatolites and microfossils. Precambrian Research 158:141–155.</ref><ref name="Origin2">Schopf, JW (2006). Fossil evidence of Archaean life. Philos Trans R Soc Lond B Biol Sci 29;361(1470) 869-85.</ref><ref name="RavenJohnson2002">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia.<ref name="AP-20131113">{{#invoke:citation/CS1|citation |CitationClass=news }}</ref><ref name="TG-20131113-JP">{{#invoke:citation/CS1|citation |CitationClass=news }}</ref><ref name="AST-20131108">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Earlier physical evidences of life include graphite, a biogenic substance, in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland,<ref name="NG-20131208">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> as well as, "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia.<ref name="AP-20151019">{{#invoke:citation/CS1|citation |CitationClass=news }}</ref><ref name="PNAS-20151014-pdf">{{#invoke:Citation/CS1|citation |CitationClass=journal }} Early edition, published online before print.</ref> According to one of the researchers, "If life arose relatively quickly on Earth ... then it could be common in the universe."<ref name="AP-20151019" />

More than 99 percent of all species, amounting to over five billion species,<ref name="Book-Biology">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> that ever lived on Earth are estimated to be extinct.<ref name="StearnsStearns2000">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref><ref name="NYT-20141108-MJN">{{#invoke:citation/CS1|citation |CitationClass=news }}</ref><ref name="Newman" /> Estimates on the number of Earth's current species range from 10 million to 14 million,<ref name="MillerSpoolman2012">{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> of which about 1.2 million have been documented and over 86 percent have not yet been described.<ref name="PLoS-20110823">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>

Through evolution, species arise through the process of speciation—where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche—and species become extinct when they are no longer able to survive in changing conditions or against superior competition. The relationship between animals and their ecological niches has been firmly established.<ref name="SahneyBentonFerry2010LinksDiversityVertebrates">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> A typical species becomes extinct within 10 million years of its first appearance,<ref name="Newman">Newman, Mark. A model of mass extinction. 1997. Journal of Theoretical Biology 189: 235–252</ref> although some species, called living fossils, survive with virtually no morphological change for hundreds of millions of years.

Mass extinctions are relatively rare events; however, isolated extinctions are quite common. Only recently have extinctions been recorded and scientists have become alarmed at the current high rate of extinctions.<ref name="MSNBC">Species disappearing at an alarming rate, report says. MSNBC. Retrieved July 26, 2006.</ref> Most species that become extinct are never scientifically documented. Some scientists estimate that up to half of presently existing plant and animal species may become extinct by 2100.<ref name="Wilson">Wilson, E.O., The Future of Life (2002) (ISBN 0-679-76811-4). See also: Leakey, Richard, The Sixth Extinction : Patterns of Life and the Future of Humankind, ISBN 0-385-46809-1</ref>


Extinction sections
Intro   Definition    Causes    Mass extinctions    History of scientific understanding    Human attitudes and interests    See also   References   External links   

PREVIOUS: IntroNEXT: Definition
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