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	Cretaceous - Wikipedia, the free encyclopedia
		The Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period, about 146 million years ago (Ma), to the beginning of the Paleocene epoch of the Tertiary period (65.5 Ma).
		The Cretaceous (from Latin creta, for chalk) was named for the extensive beds of chalk (calcium carbonate deposited by the shells of marine invertebrates) found in the upper Cretaceous of Britain and adjacent continental Europe.
		Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous proceeded faced growing competition from the adaptive radiation of birds, and by the end of the period only two highly specialised families remained.
	en.wikipedia.org /wiki/Cretaceous (968 words)

	Cretaceous-Tertiary extinction event - Wikipedia, the free encyclopedia
		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.
		Extinction was more severe among those animals living in the water column than among animals living on or in the sea floor.
		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.
	en.wikipedia.org /wiki/Cretaceous-Tertiary_extinction_event (1959 words)

	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.
		The most popular theory of the final Cretaceous extinction is that one or more asteroids or comets hit the earth, lifting massive amounts of debris and sulfur in the air and blocking the sunlight from reaching the earth’s surface.
		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)

	Gibson, L. J. --- A Catastrophe with an Impact
		Extinction of many species at approximately the same stratigraphic boundary is termed a mass extinction.
		The greatest mass extinction occurred at the boundary between the Permian and the Triassic, and is used to divide Paleozoic from Mesozoic sediments.
		The cause for the extinction of the dinosaurs remains a puzzle.
	www.grisda.org /origins/17038.htm (3343 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.
		Extinctions: Cycles of Life and Death Through Time from the Hooper Virtual Paleontological Museum discusses the asteroid impact and volcano hypotheses for the end-Cretaceous extinction.
	www.pibburns.com /catastro/extinct.htm (1469 words)

	The Great Mystery: Background
		The largest would be the "Permo-Triassic" extinction, between the Permian and Triassic periods, of the Paleozoic and Mesozoic eras.
		The Nature of Extinction: Extinction is not a simple event; it is not simply the death of all representatives of a group.
		This is not to say that all extinction hypotheses are not science; many are excellent examples of good science, but a linkage of direct causation is a problem.
	www.ucmp.berkeley.edu /diapsids/extinction.html (1283 words)

	DINOSAUR EXTINCTIONS
		However, this Cretaceous extinction saw the loss of relatively few species (perhaps 15% of all families of animals perished).
		Although it is still fashionable to picture the dinosaur (and other) extinctions as a relatively specific and rapid event for which catastrophic causes might seem reasonable, it appears more likely that the late Cretaceous extinction was a much slower, long term affair.
		The third is the one that causes so much interest for dinophiles, the difference with the late Cretaceous extinctions being not the extinctions themselves, but the failure of new dinosaur species to appear.
	www.dinoruss.org /de_4/5c524c9.htm (1081 words)

	Nat' Academies Press, Effects of Past Global Change on Life (1995)
		This decline in Cretaceous nannofossils parallels that of Cretaceous planktic foraminifers in the basal 1 m of the Tertiary at Brazos.
		If we assume that all vanishing Cretaceous species became extinct at the K/T boundary and their presence in Tertiary sediments is due to reworking, then the extinction rate exceeds 100 species per year, compared to an average of 1.5 species per million years (m.y.) and 5% per m.y.
		This species extinction pattern is representative of depositional sequences that are temporally complete across the K/T boundary in low latitudes (including Caravaca, Agost, Brazos) and illustrates the absence of a near-complete mass extinction as commonly reported from the deep-sea sections that contain a hiatus.
	www.nap.edu /books/0309051274/html/72.html (11777 words)

	Cretaceous
		The Cretaceous Period is known as the "Age of Dinosaurs".
		Climates during the Cretaceous period seem to have remained fairly constant throughout with the temperature being warm and mild.
		Cretaceous reefs were made largely made up of rudists, which were large bivalves with one cone-shaped valve and the other reduced to a small lid-like structure.
	www.denison.edu /biology/bio380-2001/Cretaceous.html (2148 words)

	Paleobiology 4
		The Cretaceous period, spanning the time interval from 144 to 65 million years ago, saw the final phases of the opening of the Atlantic Ocean, as well as the northward migration of India toward its collision with Asia during the Tertiary period of the Cenozoic era.
		Among the various hypotheses to explain the extinction that closed the Mesozoic era were allergies by dinosaurs to pollen produced by flowering plants, increased radiation levels that led to male dinosaur sterility, diseases brought by migrating animals, and a gradual climate deterioration that the dinosaurs were unable to cope with.
		Their discovery of unusually high levels of the rare metal iridium at the boundary layer between the Cretaceous and the Tertiary periods led to a conclusion that the extinction was caused by a 10 km asteroid.
	www.emc.maricopa.edu /faculty/farabee/BIOBK/BioBookPaleo5.html (7757 words)

	Paleontology
		This site features a report on the historic 1891 discovery of a giant Cretaceous fossil shark (Cretoxyrhina) and the recent excavation of a similar specimen from the chalk deposits of Gove County, Kansas.
		This outline of a presentation on extinction reviews the various catastrophic events that could lead to extinction and lists the five great mass extinctions.
		This essay on mass extinction events (Ordovician, Devonian, Permian, Triassic, Cretaceous) in the geologic record is a chapter from History of Life, a book written by Richard Cowen, in which he discusses the general geologic body of knowledge surrounding each mass extinction event.
	serc.carleton.edu /research_education/cretaceous/paleontology.html (4128 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 (593 words)

	Notes: KILLED DINOSAURS
		Mammals, although they coexisted with dinosaurs during the entire Jurassic and Cretaceous periods, were exclusively small, mouse-like creatures prior to the mass extinction.
		If the Cretaceous mass extinction had not occurred, then mammals might still be small and mousey today, and the universities would be full of intelligent dinosaurs.
		The collision hypothesis states that the Cretaceous mass extinction was triggered when an asteroid (made of rock and/or metal) or a comet (made of dusty ice) struck the Earth.
	users.zoominternet.net /~matto/M.C.A.S/notes_killed_dinosaurs.htm (1362 words)

	Readings (Site not responding. Last check: 2007-10-11)
		Documenting mass extinctions II Signor and Lipps (1982) Sampling bias, gradual extinction patterns, and catastrophes in the fossil record.
		Russell (1996) The significance of the extinction of the dinosaurs.
		The Cretaceous-Tertiary extinction II Glen (1996) Observations on the mass-extinction debates Pp.
	geosrv01.bgsu.edu /Yacobucci/Geol_480_580_Ext/readings.htm (1390 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.
	space.com /scienceastronomy/planetearth/extinction_sidebar_000907.html (523 words)

	NAI: News Stories (Site not responding. Last check: 2007-10-11)
		Recent work by others has shown that the extinction at the end of the Permian was extremely rapid, like that at the end of the Cretaceous.
		Both the KT and the PT event are approximately coincident with large volcanic eruptions, although the time scale for volcanism is millions of years, not the thousands of years (or less) that account for the great dying.
		In the case of the KT (end-Cretaceous) extinction, there was a great deal of early evidence of an extraterrestrial event, beginning with the pioneering work of Luis and Walter Alvarez in the late 1970s.
	nai.arc.nasa.gov /news_stories/news_detail.cfm?ID=286 (1443 words)

	ISGS Dinosaur Extinction
		During the Jurassic and Cretaceous periods the continents were separating and oceans opening, leading to cold and changeable conditions that dinosaurs could not adapt to, and that also affected plankton and disrupted the food chain.
		During the Cretaceous period, his argument goes, a greenhouse effect for most of the period kept temperatures at a semitropical level throughout the world.
		The idea here is that extreme volcanic activity caused huge dust clouds that blocked off much of the sun's heat and light for many months, even years, leading to a dramatic drop in temperature in both land and sea and a decrease in photosynthetic activity in such organisms as marine plankton and land plants.
	www.isgs.uiuc.edu /faq/dino-faqs/pdq201-b.html (2484 words)

	Dinosaur Extinction - Enchanted Learning Software
		The latter part of the Cretaceous period was a time of high tectonic activity (continental drift) and accompanying volcanic activity.
		Toward the end of the Cretaceous, there was a drop in sea level, causing land exposure on all continents, more seasonality, and greater extremes between equatorial and polar temperatures.
		In this Cretaceous-Tertiary or K-T mass extinction (K is for Kreide, meaning chalk in German, which describes the chalky sediment layer from that time; T is for Tertiary, the next geologic period), all land animals over about 55 pounds went extinct, as did many smaller organisms.
	www.zoomdinosaurs.com /subjects/dinosaurs/extinction/Asteroid.html (1063 words)

	Lecture 38 (Site not responding. Last check: 2007-10-11)
		The mass extinction at the end of the Cretaceous represents one of the "Big Five" mass extinctions.
		The generally warm Cretaceous climate was cooling, and a global regression of the seas (fall in sea level) was occurring.
		According to some paleontologists, the pattern of fossil distribution is not consistent with an impact causing the terminal Cretaceous extinction.
	unc.edu /gform-links/courses/2001spring/geol/018/001/SLecture38.html (609 words)

	Extinction II: The Cretaceous Extinction
		The end of the Cretaceous Period (140 to 65 million years ago) is probably most famous for the extinction of the dinosaurs.
		The Cretaceous-Triassic Extinction (often called the K-T Extinction or K-T Boundary) is most famous for the extinction of the dinosaurs.
		Many invertebrate species also went extinct at this time as well, including many species of Ammonites, which were on the rebound from their decimation at the end of the Permian Period.
	www.suite101.com /article.cfm/paleontology/73078 (376 words)

	EESJ - Cretaceous/Tertiary Boundary Reading List (Site not responding. Last check: 2007-10-11)
		McLauren (1970) proposed a meteor impact as cause of a mass extinction in the Paleozoic.
		As a consequence, scientists tended have a simplistic view of the evidence and questions outside their specialties, and this shaped the course of the interdisciplinary debate.
		Her prime example is that non-biologists held an oversimplified view (at the popular science or children's literature level) of the paleobiological evidence from the fossil record.
	www.ldeo.columbia.edu /edu/eesj/casestudies/EESJktbound.html (1255 words)

	Causes of the Cretaceous Extinction (Site not responding. Last check: 2007-10-11)
		The End-Cretaceous mass extinction has generated considerable public interest in recent years, in response to the controversial debates in the scientific community over its cause.
		Evidence that volcanism was a primary extinction agent at this boundary is also relatively strong.
		Thus at present, both the volcanic and meteorite impact hypotheses are both viable mechanisms for producing the Cretaceous mass extinction, although the latter is more popular.
	park.org /Canada/Museum/extinction/cretcause.html (418 words)

	Cretaceous (Site not responding. Last check: 2007-10-11)
		Throughout the Triassic, Jurassic, and Cretaceous periods, although life forms were present and quite abundant, there was not much diversity of species.
		This has been one of the hypotheses for the extinction of all these organisms but there could have been many different causes for their extinction.
		If it were not for the mass extinction of Cretaceous period, human beings would not exist today.
	www.bol.ucla.edu /~adamsean/Cretaceous.htm (912 words)

	BBC NEWS \| Science/Nature \| No fiery extinction for dinosaurs
		Each of these sites records a geological boundary dividing the end of the Cretaceous period from the beginning of the Tertiary.
		This Cretaceous-Tertiary boundary, or K-T boundary, marks the extinction of the dinosaurs and is thought to be associated with the impact of a large space object because the sedimentary rocks of this layer contain large quantities of the element iridium, which is most commonly found in meteorites.
		She and her colleagues looked for traces of charcoal in these rocks, which could only have been produced by burning biomass, such as vegetation.
	news.bbc.co.uk /1/hi/sci/tech/3295539.stm (725 words)

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