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Topic: Mass extinction events

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	Extinction event - Wikipedia, the free encyclopedia
		Though there were undoubtedly mass extinctions in the Archean and Proterozoic, it is only during the Phanerozoic Eon that the emergence of bones and shells in the evolutionary tree has provided a sufficient fossil record from which to make a systematic study of extinction patterns.
		The impact is postulated to have been the cause of the P-T extinction event and possibly to have initiated the break-up of the Gondwana supercontinent, creating the tectonic rift that began Australia's migration northward, away from Antarctica.
		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.
	en.wikipedia.org /wiki/Mass_extinction_events (1859 words)

	Late Devonian extinction - Wikipedia, the free encyclopedia
		The Late Devonian extinction was one of five major extinction events in the history of the Earth's biota.
		Nor is it clear whether it concerned two sharp mass extinctions or a cumulative sequence of several smaller extinctions, though the most recent research suggests multiple causes and a series of distinct extinction pulses through an interval of some three million years [1] [2].
		The most important group to be affected by this extinction event were the reef-builders of the great Devonian reef-systems, including the stromatoporoids, and the rugose and tabulate corals.
	en.wikipedia.org /wiki/Late_Devonian_extinction (810 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.
		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.
		A study was put forward by Raup and Sepkoski that suggests an extinction event of some magnitude occurs about every 26 million years, leading to some to speculate about an unknown planet whose eccentric orbit passes through the Oort cloud every 26 million years or so, causing an increased likelihood of asteroid impacts.
	www.wisegeek.com /what-are-extinction-events.htm (750 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 (4722 words)

	Conclusions -- Mass Extinction Events
		The extinction record itself is similar to the punctuated equilibrium pattern in that long stretches of low extinction rates (background rate) are interspersed with mass extincion events, which are analagous to Eldredge and Gould's rapid speciative bursts.
		Another interesting facet of the relationship between mass extinction events and evolution is that there is very often no correlation between a species' ability to survive under "usual" environmental conditions and its ability to persist through mass extinction events.
		One adaptation that may be helpful in times of mass extinction is a tolerance for lower temperatures, since climactic cooling is thought to have played a role in at least several mass extinctions.
	www.earth.rochester.edu /ees207/Mass_Ext/higgins_mass5.html (462 words)

	Dinosaur Extinction - Enchanted Learning Software
		Mass extinctions have occurred periodically throughout the existence of life on Earth.
		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 (602 words)

	[No title]
		Possible global catastrophic events suggested as causes of the P-T mass extinction include bolide impact, melting of gas hydrates flooding the world's atmosphere with methane, major marine regression, massive volcanism, oceanic anoxia and overturn of stagnant deep ocean waters (e.g.
		Biostratigraphic correlation of marine and terrestrial sequences has proved inadequate to answer the question of whether the mass extinction events in the sea and on land were synchronous or not, or if the extinctions took place over a very short or longer time period.
		Extinction of Permian marine faunas in South China has been shown to have occurred in three phases, two earlier phases in the uppermost Permian and one other phase in the earliest Triassic (Yin et al., 1996).
	www-personal.une.edu.au /~imetcal2/PTBound.html (815 words)

	Presentations and Speakers
		Extinctions are followed by recovery, and the patterns of biological and ecological recovery are a new field of study.
		The mass extinction at or near the end of the Ordovician has no iridium spike associated with it, and seems to be closely linked with a major climatic change.
		The extinction at 250 Ma, the end of the Permian, is the largest of all time: the "Mother of Mass Extinctions" according to Douglas Erwin.
	www.ucmp.berkeley.edu /education/events/cowen1a.html (1599 words)

	Devonian Times - Mass Extinction
		Scientists recognize a number of mass extinctions (extinction events that far exceed background extinction rates and are not taxonomically restricted).
		The timing and duration of the Late Devonian mass extinction(s), however, are subject to considerable debate and a variety of interpretations.
		They consider the two most extensive extinction events to be the Kellwasser Event (at the Frasnian-Famennian boundry) and the Hangeberg Event (at or near the Devonian-Carboniferous boundry).
	www.devoniantimes.org /opportunity/massExtinction.html (890 words)

	ANTARCTI
		Extinction can occur at a number of different levels from species level through all the taxonomic groups, depending on the organism’s ecology and the type of extinction event.
		The fossil record is not clear for this mass extinction event, with estimates for its duration between 500 thousand to 15 million years, and the cause being attributed to global cooling and reduced oxygen levels in shallow waters (http://www.bbc.co.uk).
		Localized extinction events on oceanic islands like Hawaii would not be well represented in the geological past because of lack of geographical distribution, population size, and endemic species which do not occur anywhere else.
	www-biol.paisley.ac.uk /courses/tatner/econs/2001/2001stud3.htm (4832 words)

	ScienceDaily: Impact Events' Kinetic Energy May Be Key To Understanding The Severity Of Mass Extinctions
		The impact energy released during the geologic ages of each extinction event is at least 10 million megatons of TNT equivalent yield per geologic age.
		Recovery From Mass Extinction Is Unexpectedly Diverse (February 27, 1998) -- A study by University of Chicago paleontologist David Jablonski shows that recoveries from mass extinctions differ widely from one geographical region to another, even though the extinction...
		Impact event -- Impact events are caused by the collision of large meteoroids, asteroids or comets (generically: bolides) with Earth and may sometimes be followed by mass extinctions of...
	www.sciencedaily.com /releases/2002/04/020409074322.htm (1647 words)

	Sixth Extinction
		The fifth mass extinction, probably caused by a giant meteor collision, occurred 65 million years ago, at the end of the Cretaceous period, and ended the reptilian dominance of the Earth.
		In an attempt to be quantitative with the known extinction data, and thereby come up with an assessment of whether or not we face a biological crisis of our own making, Stuart Pimm and two of his colleagues analyzed some of the best known and most closely documented cases.
		The documentation of known extinctions may seem to be the only way to demonstrate that we are in the midst of a biotic crisis, and this is what skeptics demand.
	www.well.com /user/davidu/sixthextinction.html (5196 words)

	NAI: Ask an Astrobiologist (Site not responding. Last check: 2007-11-01)
		Ice ages (glaciation events), volcanic eruptions, and changes in sea level appear to be the most common culprits.
		The general advantage to an extinction event is that other species are allowed to proliferate due to the loss of a food source competitor or even a predator.
		The phenomenon of mass extinctions sets the stage for many questions that have yet to be answered with complete certainty.
	nai.arc.nasa.gov /astrobio/feat_questions/mass_extinction.cfm (903 words)

	Meteroites, Impacts, & Mass Extinction
		While the meteorite impact theory of mass extinctions has become accepted by many scientists for particular extinction events, there is still considerable controversy among scientists.
		Still, because of their are many other possibilities for the cause of mass extinctions, please read your book for the arguments against the impact theory.
		The mass extinction at the end of the Mesozoic Era, that is the Cretaceous - Tertiary boundary (often called the K-T boundary) 65 million years ago, shows much evidence that it was related to an impact with an extraterrestrial object.
	www.tulane.edu /~sanelson/geol204/impacts.htm (4620 words)

	SPACE.com -- The Five Worst Extinctions in Earth's History (Site not responding. Last check: 2007-11-01)
		Here are details of the five worst mass extinctions in Earths history and their possible causes, according to paleobiologist Doug Erwin of the Smithsonian Institutions National Museum of Natural History.
		The extinction killed 16 percent of marine families, 47 percent of marine genera (the classification above species) and 18 percent of land vertebrate families, including the dinosaurs.
		The Permian-Triassic catastrophe was Earths worst mass extinction, killing 95 percent of all species, 53 percent of marine families, 84 percent of marine genera and an estimated 70 percent of land species such as plants, insects and vertebrate animals.
	space.com /scienceastronomy/planetearth/extinction_sidebar_000907.html (465 words)

	ScienceDaily: Methane Thought To Be Responsible For Mass Extinction
		The mechanism also might explain other extinctions and climate perturbations (ice ages) and even the Biblical flood, as well as be the cause of future catastrophes.
		New Evidence Indicates Biggest Extinction Wasn't Caused By Asteroid Or Comet (January 23, 2005) -- For the last three years evidence has been building that the impact of a comet or asteroid triggered the biggest mass extinction in Earth history, but new research from a team headed by a University...
		Impact Events' Kinetic Energy May Be Key To Understanding The Severity Of Mass Extinctions (April 10, 2002) -- The kinetic energy created by asteroid and comet impacts with the Earth may be key to linking some impacts with mass extinction events.
	www.sciencedaily.com /releases/2003/08/030828071722.htm (1547 words)

	Mass Extinction Looms
		Peter Raven, director of the Missouri Botanical Garden and an expert in plants, believes there is evidence that the Earth has gone through five mass extinction events in the past, and that it is well on the way to number six.
		In each of the prior mass extinctions, Raven noted that somewhere between one-fourth and one-half of all species died over the course of a few million years.
		In the past, he said, the extinction events were caused by natural phenomenon.
	perdurabo10.tripod.com /id108.html (1138 words)

	SPACE.com -- Huge Space Clouds May Have Caused Mass Extinctions
		Giant space clouds of gas may have changed the climate or atmosphere on Earth and fueled mass extinctions millions of years ago, scientists said Thursday.
		A widespread die-off 65 million years ago, which wiped out the dinosaurs and many other species, is thought by most scientists to have been caused by an asteroid impact.
		Extra cosmic rays produced during such an event, owing to interactions of the interstellar dust with the Sun, would break up nitrogen molecules in Earth's atmosphere, leading to ozone destruction.
	www.space.com /scienceastronomy/050503_mass_extinctions.html (506 words)

	Previous Mass Extinctions-it Came from Below
		Siberian "traps", the researchers theorize that it was enough to tip the atmospheric balance into the "unsustainable" range for most life at the time and help bring about the extinction event.
		The idea that meteorite impacts caused mass extinctions has been in vogue over the last 25 years, since Louis Alverez’s research team in Berkeley, California published their work about an extraterrestrial iridium anomaly found in 65-million-year-old layers at the Cretaceous-Tertiary boundary.
		There is scant evidence of impacts at the time of other major extinctions e.g., at the end of the Permian, 250 million years ago, and at the end of the Triassic, 200 million years ago.
	technocrat.net /d/2006/3/29/1787 (856 words)

	Researchers uncover secret to mass extinction events
		The same pattern was occurring worldwide, marking the largest global mass extinction since the dinosaurs disappeared.
		Their findings are based on an analysis of the chemical composition of fossilized "ear stones," called otoliths, from a group of fish that survived the mass extinction event.
		In fact, "this is the first time anyone has looked at seasonality as a variable for an extinction event across a geological time boundary," Patterson adds.
	www.eurekalert.org /pub_releases/2000-10/UoM-Rust-1710100.php (644 words)

	Open Questions: Mass Extinctions
		Describes how an asteroid impact may have caused the release of methane which ignited, caused a global firestorm, and led to a mass extinction event.
		Nice overview of the various mass and minor extinction events in Earth's history, with speculation as to possible causes.
		General information on the impact event which thought to have caused the mass extinction 65 million years ago.
	www.openquestions.com /oq-ge008.htm (298 words)

	CCNet-10-03-2006
		Understanding the extinction and recovery processes in ancient events, especially those associated with global warming, may be crucial to managing the present biodiversity crisis.
		In the past 25 years the study of these mass extinction events has increased dramatically, with most focus being on the Cretaceous–Tertiary (K–T) event, although study of the end-Permian event (in terms of research output) is likely to surpass that of the K–T in the next few years.
		However, the case for the latter mechanism as an extinction trigger is considerably weakened by data from the recent geological past, showing that no major marine extinction occurred with the advance and retreat of the Pleistocene ice caps (Newell, 1962 and Valentine and Jablonski, 1991).
	www.staff.livjm.ac.uk /spsbpeis/CCNet-10-03-06.htm (5078 words)

	context weblog :: late permian mass extinction
		While we remain unsure of their number, there is general agreement over the existence of major extinction events: limit Ordovician-Silurian (about 440 million years ago), Late Devonian (about 360 million years ago), limit Permian-Triassic (about 250 million years ago), Late Triassic (about 210 million years ago), limit Cretaceous-Tertiary (about 65 million years ago).
		Now is widely believed that the Chicxulub structure represents a large meteorite impact that was responsible for the mass extinctions of 65 million years ago, the time of the dinosaur extinction.
		In February 22, 2001, was announced this new tool allowed research team's new findings about the mass extinction 250 million years ago (Permian-Triassic boundary), the Earth1s worst mass extinction, killing 95 percent of all species.
	www.straddle3.net /context/01/010227.en.html (1300 words)

	School of Earth and Environment (Site not responding. Last check: 2007-11-01)
		Evidence for marine anoxia is often associated with all of these extinction events and this nicely overlaps with Professor Wignallâs other main research interest: the characterisation of fl shale depositional environments.
		As many of the key extinction boundary sections are not found in West Yorkshire, Professor Wignall has been forced to travel to often remote parts of the globe: his favourite field areas to date have been Nevada and central Poland.
		Wignall, P.B. The end-Permian mass extinction, Mercian Geologist, 15, pp.251.
	www.see.leeds.ac.uk /people/p.wignall (1545 words)

	Many entire galaxies (including our own) could have been fully colonized twice by the end of this period; Earth may be ...
		The distance the mystery mass orbits from the Sun helps determine how large it is. The further out along the edges of the system it is, the larger it must be to have the detected effect (perhaps being as much as half the mass of the Sun).
		By contrast, the mass extinctions of 440 million BC and 365 million BC killed off a majority of marine species; the first perhaps by substantial changes in sea levels, and the second maybe by global cooling and a reduction of available oxygen in the seas.
		Events which might bring about a sufficient mass shift without calamitous extinctions might include a massive earthquake rupturing the crust undersea, allowing a huge volume of seawater to be swallowed up by the mantle, in a way much more sudden than the normal subduction process.
	www.jrmooneyham.com /genes2.html (13920 words)

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