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Topic: Mass extinctions

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	mass extinction. The Columbia Encyclopedia, Sixth Edition. 2001-05
		The best-known mass extinction is that at the end of the Cretaceous period, when the dinosaurs and many other plants and animals disappeared and up to 75% of all marine genera were lost.
		Theories regarding the causes of mass extinctions abound and are the subject of intense study and debate.
		The extinctions, however, did not conform to the usual evolutionary rules regarding who survives; the only factor that appears to have improved a family of organisms’ chance of survival was widespread geographic colonization at the time of the event.
	www.bartleby.com /65/ma/massex.html (740 words)

	Catastrophism and Mass Extinctions
		Asteroids of Death by E.S. Matalka discusses the asteroid impact hypothesis for the extinction of the dinosaurs.
		Carriers of Extinction by Carl Zimmer suggests that the megafaunal extinctions at the end of the last ice age were caused by pathogens carried by migrating humans.
		Mass Extinctions deals with the dinosaur extinction as well as mass extinctions in general.
	www.pibburns.com /catastro/extinct.htm (1469 words)

	Evolution, Mass Extinctions, and Mass Speciations
		There would be the extinction of large fraction of the Earth's animals, plants and microorganisms, including the mass extinction of plankton, genetic mutation, nutrient dumping, climatic cooling, wildfires, hydrocarbons, acid rain, soot, and shocked and/or irradiated minerals.
		Mass extinctions are not random and are not related to an organism's ability to survive.
		Mass extinctions of four-footed land animals (tetrapods) are not as great as marine extinctions, nor are the extinctions due to a decrease in fitness.
	www.livingcosmos.com /evolution.htm (5631 words)

	Mass Extinction - In The Wild Spotlight - Bagheera
		Mass extinctions are episodes in the history of life on Earth during which unusually large numbers of species die off.
		The five mass extinction episodes occurred because of major changes in the prevailing ecological conditions brought about by climate change, cataclysmic volcanic eruptions, or collisions with giant meteors.
		The sixth mass extinction appears to be in progress now, and the main cause is environmental change brought about by human activities.
	www.bagheera.com /inthewild/spot_massextinctions.htm (168 words)

	Introduction to Mass Extinction Events
		The background extinction rate is the relatively constant rate at which organisms have been disappearing from the fossil record over the course of geological time and has been variously estimated at between five and ten marine families per million years.
		Mass extinctions are often sifnifiers of large-scale climatic, environmental changes, often global in nature.
		Mass extinctions often leave behind a great deal of unused niche space and the opportunity for adaptive radiation is great.
	www.earth.rochester.edu /ees207/Mass_Ext/higgins_mass2.html (773 words)

	An On-going Process
		A mass extinction is any substantial increase in the amount of extinction (i.e., lineage termination) suffered by more than one geographically widespread higher taxon during a relatively short interval of geologic time, resulting in an at least temporary decline in their standing diversity [numbers of species].
		Background extinctions are at the opposite end of the spectrum from mass extinctions.
		The fact that today's extinction rate vastly exceeds any estimation of the background extinction rate impels many scientists to conclude that we are now on the cusp of the so-called Sixth Extinction.
	www.amnh.org /science/biodiversity/extinction/Intro/OngoingProcess.html (389 words)

	Extinction (Site not responding. Last check: 2007-11-07)
		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 (4478 words)

	BBC Evolution Weekend: Extinction Files - Mass Extinctions (Site not responding. Last check: 2007-11-07)
		It is often difficult to determine exactly when mass extinction events have occurred in the Earth's history - the fossil record is not perfect, and the poorer the record for a particular time frame, the more it is open to different interpretations.
		Some scientists have suggested that there is a cycle of mass extinctions, with a major die off every 26 million years or so.
		This would imply that there have been some 23 extinction events since the Cambrian, a figure which is at the upper limit of most estimates.
	www.bbc.co.uk /education/darwin/exfiles/massintro.htm (118 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)

	DinoData Paleozoica (Site not responding. Last check: 2007-11-07)
		A mass extinction is most simply defined as a period of time in which the number of extinctions drastically rises (Raup 801).
		The extinction of the dinosaurs is a classic example, but this episode is not the only mass extinction recorded in the fossil record.
		The second major terrestrial theory of periodic mass extinction causes is the hypothesis of glaciation.
	www.dinodata.net /DNM/what.htm (2895 words)

	mass extinctions
		The definition of mass extinction is somewhat difficult because the word 'catastrophe' is almost always used in relation to human life or property loss, whereas until recently mass extinctions were events outside human experience and influence.
		For the extinction at the end of the Cretaceous, for instance, we have no independent evidence whether the main phase of extinction took anywhere between several 10,000s of years or a few seconds.
		Our best estimates of rates of extinction during the mass extinctions of the fossil record suggest that these present rates are comparable to those during mass extinctions.
	ethomas.web.wesleyan.edu /ees123/mass_extinctions.htm (2456 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)

	BBC Evolution Website: Extinction Files (Site not responding. Last check: 2007-11-07)
		Extinction is, quite literally, the end of a particular evolutionary line, the end of a species, a family, or a larger group of organisms.
		Extinctions, mostly at the level of species, have been occurring constantly at a low 'background rate', usually matched by the rate at which new species appear - with the result that biodiversity is constantly increasing.
		these are the mass extinctions, when more than 50% of the Earth's species vanish in the geological instant of a few million years.
	www.bbc.co.uk /education/darwin/exfiles/index.htm (149 words)

	The Evolution of Mass Extinctions (Site not responding. Last check: 2007-11-07)
		Being the most recent mass extinction, thousands of scientists around the world have investigated it, and elementary school children are familiar with it.
		Researchers believe, for example, that the second of the mass extinctions, during the Late Devonian continued for a period of 20-25 million years, beginning with a lingering marine crisis.
		The study of these five mass extinctions can have a profound effect on our understanding of what is happening around us, but the research can only be useful if we do something about it.
	www.priweb.org /ed/ICTHOL/ICTHOL04papers/43.htm (1498 words)

	Geological Society - Teaching Resources - Flood Basalts, Mantle Plumes and Mass Extinctions (Site not responding. Last check: 2007-11-07)
		Extinction events are increasingly seen as important factors in the history of life on Earth, and recent studies suggest catastrophic causes for at least some mass extinctions.
		If there is a causal link between flood basalt events and mass extinctions, it may lie in the environmental impact of the gases released, because basalt eruptions are not particularly explosive.
		Although the correlation between some flood basalt episodes and extinctions may implicate volcanism in the extinctions, it is also possible that other factors lead to an apparent association.
	www.geolsoc.org.uk /template.cfm?name=fbasalts (1166 words)

	SPACE.com -- The Five Worst Extinctions in Earth's History
		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.
	www.space.com /scienceastronomy/planetearth/extinction_sidebar_000907.html (508 words)

	GEOL 308: Extinctions
		Mass Extinctions are periods of time when a species death rate greatly exceeds its origination rate.
		In order to be defined as a "mass" extinction, 10-20% of all marine families must go extinct.
		This correlates with extinctions because scientists today fear that we may be in the midst of a sixth mass extinction event because of an alarming decrease in the biodiversity of certain ecosystems.
	geoweb.tamu.edu /courses/geol308/extinctions.html (216 words)

	“Survivor” Mass Extinction Style: UC Geologist Reveals Bust and Boom Cycles
		Mass extinctions may have a silver lining, reports University of Cincinnati geologist Arnold Miller in the Nov. 7 Science.
		The bust is a mass extinction event, caused by events such as an ice age or an asteroid hitting the earth.
		This will permit him to investigate directly whether the longer-lived genera that originated after mass extinctions really were more widespread, as predicted, than their shorter-lived counterparts.
	www.uc.edu /news/NR.asp?id=1075 (633 words)

	"The Sixth Extinction" by Niles Eldredge, Ph.D.
		There is little doubt left in the minds of professional biologists that Earth is currently faced with a mounting loss of species that threatens to rival the five great mass extinctions of the geological past.
		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 (2665 words)

	Nemesis, Proposed Companion Star to the Sun and Mass Extinctions on Earth
		Although the means of triggering massive extinctions are essentially the same, this second group believes the companion star is invisible: either a brown dwarf, a star so tiny that it never ignited, or a fl hole, a shrunken star so dense that its gravity prevents any light from escaping.
		In accordance with the conservation of angular momentum, the redistribution of mass alters the rotation rate of the Earth’s crust and mantle with respect to the liquid core and leads to a disruption of the magnetic field.
		The presence of an iridium anomaly in craters that correspond to mass extinctions, and in volcanic rocks and sea beds that correspond to geomagnetic reversals would be a strong supporting argument for the occurrence of comet storms.
	www.lbl.gov /Science-Articles/Archive/extinctions-nemesis.html (4559 words)

	Historic Mass Extinctions
		A mass extinction is recognized as an interval of one to several million years where an unusually high number of "unrelated groups from a number of habitats, terrestrial as well as marine" become extinct.
		There is substantial evidence (iridium anomalies, craters, and shattered quartz fragments) to support such theories and there is good reason to believe that such an impact could create conditions (shock waves, tsunamis, forest fires, acid rain, darkness lasting months or years, global cooling or warming) to eliminate a large portion of the world's species.
		Other leading theories to causes of mass extinctions include: global climate change, changes in sea level, chemical poisoning of the atmosphere and/or oceans, variation in solar radiation, and extreme volcanic activity.
	www.mongabay.com /09mass_x.htm (301 words)

	Mass Extinctions
		On the land, while animal life is eliminated repeatedly, plants tend to be more highly resistant to mass extinctions.
		Each agent of mass extinction is presumed to have caused massive changes in the environment that resulted in extinctions of species and life.
		However, more information is required to see if the level of extinctions being experienced today is a harbringer of a mass extinction or merely reflect natural background levels of species replacement.
	fig.cox.miami.edu /~cmallery/150/astrobiol/mass_extinctions.htm (450 words)

	SPACE.com -- Controversial New Claim in Death-by-Asteroid Case
		Volcanic activity remains a suspect in the extinction cases, and a growing scientific minority is skeptical of the whole death-by-space-rock scenario.
		"It appears to us that the two largest mass extinctions in Earth history [65 million and 251 million years ago] were both caused by catastrophic collisions with chondritic meteoroids," the researchers write.
		Researchers agree that at some time near the dinosaur extinction event 65 million years ago, a vast outpouring of volcanic material created a feature in India called the Deccan Traps, a bed of lava that covers an area about the size of Oregon and Washington states combined.
	www.space.com /scienceastronomy/mass_extinction_031120.html (854 words)

	You Can Run, But You Can’t Hide: Mass Extinctions Spare No One
		The two scientists studied the survivorship of 350 evolutionary lineages of marine mollusks –clams and other two-shelled ocean-dwellers– during the mass extinction event that killed the dinosaurs at the close of the Cretaceous Period, 65 million years ago.
		Scientists had believed, for example, that larger-bodied organisms fared worse in mass extinctions than organisms that were simply smaller in size.
		Maybe this change in the rules for extinction or survival helps to explain why the dinosaurs are gone and mammals weathered the end-Cretaceous extinction.
	www-news.uchicago.edu /releases/95/950417.mass.extinctions.shtml (711 words)

	Asteroid and Comet Impact Craters and Mass Extinctions
		Mass Extinction and Rise of Dinosaurs Tied to Cosmic Collision.
		Basaltic volcanism and mass extinction at the Permo-Triassic boundary: Environmental impact and modeling of the global carbon cycle.
		Chicxulub impact is the KT killer that caused the mass extinction.
	www4.tpg.com.au /users/tps-seti/crater.html (4305 words)

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