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Topic: Extinction event

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	Bagheera: An Endangered Species and Endangered Animal Online Education Resource
		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.
	www.bagheera.com /inthewild/ext_background.htm (935 words)

	What are Extinction Events?
		Extinction events, or extinction-level events (ELE), are caused by global environmental disruptions that result in large percentages of marine and terrestrial species dying out.
		Also referred to as the KT event, from the German spelling of the geologic time periods, this extinction event was believed to be caused by an asteroid impact in what is now the Gulf of Mexico.
		This extinction event is thought to have similar causations as the previous event, with massive volcanic eruptions of the Central Atlantic Magmatic Province (CAMP) leading to possible methane gasification.
	www.wisegeek.com /what-are-extinction-events.htm (750 words)

	Extinction event - Biocrawler (Site not responding. Last check: )
		Extinction events also occurred during the Proterozoic and Archaean Eons, but these earlier events are less well documented.
		The Big Five are the Ordovician-Silurian extinction events, the Late Devonian extinction, the Permian-Triassic extinction event, the Triassic-Jurassic extinction event and the Cretaceous-Tertiary extinction event.
		The collision of a large asteroid, or other impact event, with the earth is one of several hypothetical scenarios put forward in recent years that scientists believe may cause or trigger an extinction event (another is global nuclear warfare).
	www.biocrawler.com /encyclopedia/Extinction_event (936 words)

	Cretaceous-Tertiary extinction event - Biocrawler (Site not responding. Last check: )
		The end of the Cretaceous coincided with the end of the dinosaurs and was in general a period of extraordinary mass extinction, leading to the Tertiary Period of the Cenozoic Era, in which mammals came to dominate on Earth.
		Another proposed cause for the K-T extinction event was cosmic radiation from a relatively nearby supernova explosion.
		Previous extinction events have included the Triassic-Jurassic extinction event and the Permian-Triassic extinction event, which is the largest extinction event ever recorded.
	www.biocrawler.com /encyclopedia/Cretaceous-Tertiary_extinction_event (1514 words)

	NationMaster - Encyclopedia: Triassic
		The extinction event that closed the Triassic period has recently been more accurately dated, but as with most older geologic periods, the rock beds that define the start and end are well identified, but the exact dates of the start and end of the period are uncertain by a few million years.
		An extinction event (also extinction-level event, ELE) occurs when there is a sharp decrease in the number of species in relatively short period of time.
		The Triassic period ended with a mass extinction, which was particularly severe in the oceans; the conodonts disappeared, and all the marine reptiles except ichthyosaurs and plesiosaurs.
	www.nationmaster.com /encyclopedia/Triassic (736 words)

	Kids.Net.Au - Encyclopedia > Holocene extinction event
		The Holocene extinction event is the name given to the widespread extinction of species occurring in the modern era, some defining the start of the era with the dying off of the species Homo neanderthalensis.
		The rate of extinction today appears to be similar to, or perhaps greater than, the rate during "classic" extinction events in the past, such as the one between the Devonian period and Carboniferous.
		Even those that were caused by sudden events, such as an asteroid impact, take a long time due to the complex ecological interactions that are upset by the event.
	www.kids.net.au /encyclopedia-wiki/ho/Holocene_extinction_event (373 words)

	Holocene extinction event - Definition, explanation
		Extinction rates are minimized in the popular imagination by the survival of captive trophy populations of animals that are merely "extinct in the wild," (Père David's Deer, etc) and by marginal survivals of highly-publicized megafauna that is "ecologically extinct" (Giant Panda, Sumatran Rhinoceros, the North American Black-Footed Ferret, etc.).
		Even those extinction events that were caused by instantaneous events -- the Chicxulub asteroid impact being currently the demonstrable example -- unfold through the equivalent of many human lifetimes, due to the complex ecological interactions that are unleashed by the event.
		Those who are skeptical about the impending mass extinction argue that even if the current rate of extinction is higher than the rate during a great mass extinction event, as long as the current rate does not last more than a few thousand years, the overall effect will be small.
	www.calsky.com /lexikon/en/txt/h/ho/holocene_extinction_event.php (1336 words)

	Armageddon Online - Extinction Event, Extinction Level Event, ELE
		This was not a sudden event; evidence suggests that the extinctions took place over a period of some three million years.
		For example, the Cretaceous-Tertiary extinction event promoted the domination of spores and swamp life for a period almost directly after the event.
		The collision of a large asteroid with the earth is one of several hypothetical scenarios put forward in recent years that scientists believe may cause or trigger an ELE (another is global nuclear warfare).
	www.armageddononline.org /extinction_event.php (769 words)

	Sea Shepherd - The Beginning of the End for Life as We Know it on Planet Earth?
		The most recent event was 65 million years ago at the end of the Jurassic period, a cataclysmic occurrence that exterminated the dinosaurs, the dominant group of species at of that period.
		The world after the Holocene extinction event, the one we are in now, will be as radically altered and most likely one of the species that will not survive the event will be the present dominant species — the human species.
		Extinction of marine wildlife is considered to be even more severe with only 4% of the Northern cod remaining and sharks being removed from the sea at a rate of one hundred million a year.
	www.seashepherd.org /editorials/editorial_070504_1.html (2730 words)

	Extinction
		Extinction strikes in both the land and the sea, though higher rates are generally cited among marine forms.
		An unresolved question is whether mass extinction events represent a vastly increased rate of natural selection, in which the least well-adapted organisms are killed preferentially, or whether they are the result of catastrophic change that randomly eliminates taxa regardless of adaptation (Brenchley 2002).
		However, other researchers observe that a mass extinction event is not necessary to explain the disappearance of the Ediacarans from the fossil record; conditions may simply have ceased to be favourable to their preservation with the arrival of more numerous and more diverse scavenging and bioturbating organisms.
	www.peripatus.gen.nz /paleontology/extinction.html (4728 words)

	Extinction event
		An extinction event (also extinction level event, ELE) is a period in time when a large number of species died out.
		The normal background rate of extinctions is about two to five families of marine invertebrates and vertebrates every million years.
		A recent theory, which has been largely discredited, suggested that the extinction cycle is caused by the orbit of a companion star which periodically disturbs the Oort cloud, sending storms of large asteroids and comets towards the Solar System every 26 million years.
	www.ebroadcast.com.au /lookup/encyclopedia/ex/Extinction_event.html (416 words)

	Cretaceous-Tertiary extinction event at AllExperts
		The extinction event is also known as the K-T extinction event and its geological signature as the KT boundary ("K" is the traditional abbreviation for the Cretaceous period, named from the Latin for chalk, creta, which in Greek is kreta.
		The KT extinction event, labeled here as "End K", is shown in comparison to the impact of other events on the extinction intensity for marine fossilerferous genera.
		Another proposed cause for the K-T extinction event was cosmic radiation from a relatively nearby supernova explosion.
	en.allexperts.com /e/c/cr/cretaceous-tertiary_extinction_event.htm (2193 words)

	Extinction Events
		This event, responsible for the demise of the Vendian organisms, may have been reponsible for the ensuing diversification of the Cambrian shelly fauna.
		The most important group to be affected by this extinction event were the major reef-builders including the stromatoporoids, and the rugose, and tabulate corals.
		According to this theory,the extinction of the Devonian was triggered by another glaciation event on Gondwana, as evidenced by glacial deposits of this age in northern Brazil.
	www.lakepowell.net /sciencecenter/extinction_events.htm (1939 words)

	Permian-Triassic extinction event - Definition, explanation
		The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 252 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods.
		Organisms throughout the world, regardless of habitat, suffered similar rates of extinction, suggesting that the cause of the event was a global, not local, occurrence, and that it was a sudden event, not a gradual change.
		Many theories have been presented for the cause of the extinction, including plate tectonics, an impact event, a supernova, extreme volcanism, the release of frozen methane hydrate from the ocean beds to cause a greenhouse effect, or some combination of factors.
	www.calsky.com /lexikon/en/txt/p/pe/permian_triassic_extinction_event.php (2075 words)

	Spartanburg SC \| GoUpstate.com \| Spartanburg Herald-Journal (Site not responding. Last check: )
		The Permian-Triassic (P-Tr) 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.
		It was the Earth's most severe extinction event, with about 96 percent of all marine species and 70 percent of terrestrial vertebrate species becoming extinct.
		Evidence that an impact event caused the Cretaceous-Tertiary extinction event has led naturally to the speculation that impact may have been the cause of other extinction events, including the P-Tr extinction, and the consequent search for evidence of impact at other extinction horizons and for large impact craters of the appropriate age.
	www.goupstate.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=Permian-Triassic_extinction_event (3253 words)

	Palaeos Ecology : Extinction : Extinction (Site not responding. Last check: )
		Although the Cretaceous-Tertiary event is by far the most widely familiar – on account of its association with the ever-popular dinosaurs and Alvarez' exciting platinum/iridium evidence for the role of a major meteor impact – the event at the end of the Permian was by far the most profound.
		An unresolved question is whether mass extinction events represent a vastly increased rate of natural selection, in which the least well-adapted organisms are killed preferentially, or whether they are the result of catastrophic change that randomly eliminates taxa regardless of adaptation (Brenchley 2002).
		However, other researchers observe that a mass extinction event is not necessary to explain the disappearance of the Ediacarans from the fossil record; conditions may simply have ceased to be favourable to their preservation with the arrival of more numerous and more diverse scavenging and bioturbating organisms.
	www.palaeos.com /Ecology/Extinctions/Extinction.html (4100 words)

	Cretaceous-Tertiary extinction event Summary
		Extinction was more severe among those animals living in the water column than among animals living on or in the sea floor.
		It was in general a period of extraordinary mass extinction, leading to the Tertiary Period of the Cenozoic Era, in which mammals came to dominate on Earth.
		Previous extinction events have included the Cambrian-Ordovician extinction, End Ordovician, Triassic-Jurassic, Late Devonian and the Permian-Triassic, which is the largest extinction event ever recorded.
	www.bookrags.com /Cretaceous-Tertiary_extinction_event (3534 words)

	Extinction at AllExperts
		The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to breed and recover may have been lost before this point; see population bottleneck).
		This is known as the Holocene extinction event and is at least the sixth such extinction event.
		Extinction is an important research topic in the field of zoology, and biology in general, and has also become an area of concern outside the scientific community.
	en.allexperts.com /e/e/ex/extinction.htm (2974 words)

	Extinction - Great Dying - Crystalinks
		Extinction of a species may come suddenly when an otherwise healthy species is wiped out completely, as when toxic pollution renders its entire habitat unlivable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out competition for food to newer, better adapted competitors.
		Human extinction would be the extinction of the human species, Homo sapiens, whether on Earth (often as the result of a doomsday event) or from the entire universe, provided the species colonizes on other planets.
		Fear of human extinction is said to be one of the motivating factors of the environmentalist movements of the 20th and 21st century.
	www.crystalinks.com /extinction.html (3544 words)

	News \| TimesDaily.com \| TimesDaily \| Florence, AL (Site not responding. Last check: )
		The large number of extinctions span numerous families of plants and animals including mammals, birds, amphibians, reptiles and arthropods; a sizeable fraction of these extinctions are occurring in the rainforests.
		Extinction rates are minimized in the popular imagination by the survival of captive trophy populations of animals that are merely "extinct in the wild," (PÃ¨re David's Deer, etc) and by marginal survivals of highly-publicized megafauna that is "ecologically extinct" (Giant Panda, Sumatran Rhinoceros, the North American Black-Footed Ferret, etc.) and by unregarded extinctions among arthropods.
		Even those extinction events that were caused by instantaneous events — the Chicxulub asteroid impact being currently the demonstrable example — unfold through the equivalent of many human lifetimes, due to the complex ecological interactions that are unleashed by the event.
	www.timesdaily.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=Holocene_extinction_event (2114 words)

	The Sixth Extinction by Niles Eldredge, Ph.D.
		The major global biotic turnovers were all caused by physical events that lay outside the normal climatic and other physical disturbances which species, and entire ecosystems, experience and survive.
		At first glance, the physically caused extinction events of the past might seem to have little or nothing to tell us about the current Sixth Extinction, which is a patently human-caused event.
		The invention of agriculture accelerated the pace of the Sixth Extinction.
	www.actionbioscience.org /newfrontiers/eldredge2.html (2629 words)

	Dinosaur Extinction - Enchanted Learning Software
		The extinctions are clustered in a short amount of geological time (a few million years is very short in terms of geological time).
		The nemesis hypothesis of Raup and Sepkoski theorizes that there is a periodicity of 26 million years to mass extinctions which is caused by collisions with comets from the Oort cloud as they are perturbed in their orbits by a dark star (a companion star to the sun).
		The other dinosaur species died out during the several mass extinctions that occurred in the Mesozoic: at the end of the Triassic (213 million years ago), during and at the end of the Jurassic (at 190, 160, 144 mya), and during and at the end of the Cretaceous (at 120, 82, and 65 mya).
	www.enchantedlearning.com /subjects/dinosaurs/extinction/index.html (602 words)

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