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Topic: Extinction (astronomy)

	Astronomy Encyclopedia (Site not responding. Last check: 2007-10-19)
		A traditional division of astronomy is given by the region of the electromagnetic spectrum observed.
		One of the oldest fields in astronomy, and in all of science, is the measurement of the positions of celestial objects in the sky.
		Astronomy is the scientific study of the universe as a whole, and of celestial bodies and the underlying physics governing these bodies.
	www.hallencyclopedia.com /topic/Astronomy.html (5634 words)

	Evolution: Extinction: A Modern Mass Extinction?
		The current mass extinction has been unfolding for millennia, and unlike the greenhouse effect, global warming, or the hole in the ozone, it is visible without sophisticated imagery or complex computer modeling.
		Many scientists dispute whether an extinction is currently taking place at all, or suggest that we are facing the prospect but have not yet begun the experience.
		I believe that the current extinction is well under way, having started with the dawn of the Ice Age, about 2.5 million years ago, and since then accelerating in its rate of species destruction.
	www.pbs.org /wgbh/evolution/extinction/massext/statement_04.html (461 words)

	CATHOLIC ENCYCLOPEDIA: Astronomy
		Descriptive astronomy, meanwhile took its rise from the invention of the telescope, and the facilities thus afforded for the close scrutiny of the denizens of the sky; while practical astronomy gained continually in refinement with the improvement of optical and mechanical arts.
		Greek astronomy was embodied in Ptolerny's "Almagest" (the name is of mixed Greek and Arabic derivation), composed at Alexandria about the middle of the second century A. It was based upon the geocentric principle.
		Descriptive astronomy may be said to have originated with the invention of the telescope by Hans Lippershey in 1608.
	www.newadvent.org /cathen/02025a.htm (4544 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 (602 words)

	Lecture: Interstellar Medium
		This is an extreme example of interstellar extinction which is the dimming of star light caused by the presence of interstellar material.
		Extinction is quantified in terms of so many "magnitudes" of extinction, i.e., 5 magnitudes of extinction between us and some other star means that the apparent magnitude we observe will be 5 magnitudes larger than what it would be without the interstellar medium.
		The effect of extinction is to increase the apparent magnitude number, that is to decrease the apparent brightness.
	www.astro.virginia.edu /class/hawley/astr124/ism.html (2101 words)

	Zoom Astronomy Glossary: A
		This theory is that a large asteroid, meteor, or comet hit the Earth 65 million years ago, causing huge atmospheric and geologic disruptions, leading to a mass extinction which killed the dinosaurs and many other species.
		Astronomy is the scientific study of space, including the planets, stars, galaxies, comets, and nebulae.
		Astrophysics is a branch of astronomy that studies the physical properties of celestial bodies and other matter and energy in space.
	www.zoomwhales.com /subjects/astronomy/glossary (4918 words)

	Astronomy & Space
		Extinctions -n- Events it has happened before, it will happen again Extinction Level Events / Mass Level Extinctions There have been 5 known mass level extinctions in Earth's history; these events are characterized by the marked decline of...
		Since the asteroid impact - mass extinction hypothesis first caught the attention of the scientific community and the public in 1980, an enormous amount of...
		Speculated Causes of the Permian Extinction Although the cause of the Permian mass extinction remains a debate, numerous theories have been formulated to explain the events of the extinction.
	groups.msn.com /AstronomySpace/extinctionlevelevents.msnw (665 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 (445 words)

	Working Group on Infrared Astronomy: On Improving IR photometric passbands
		Correction for atmospheric extinction is difficult in infrared photometry, notwithstanding the apparently linear form of the extinction curve at airmasses greater than 1 in some bandpasses, chiefly because of the strong and variable effects of water-vapor absorption.
		In broadband photometry, the extinction line is always more or less curved, because those wavelengths whose monochromatic extinction coefficients are largest are removed from the stellar spectrum at small air masses, leaving primarily the wavelengths with smaller extinction coefficients at larger air masses.
		If the correlation between monochromatic extinction and wavelength (and hence the correlation between effective extinction coefficient and stellar color) is small, little of this vector rotation can be transformed away with the usual color terms.
	www.ucalgary.ca /~milone/IRWG/yms/yms.html (9900 words)

	extinction - Ask.com Web Search
		The moment of extinction is generally considered to be the death of the last individual of that species.
		The Nature of Extinction: Extinction is not a simple event; it is not simply the death of all representatives of a group.
		In biology and ecology, extinction is the cessation of existence of a species or group of taxa, reducing biodiversity.
	www.ask.com /web?q=extinction (265 words)

	Periodicity in Extinction
		As Hoffman argued, because Raup and Sepkoski used “peaks” as the definition of mass extinctions, it was necessary that the number of families extinguished should be greater than in the preceding and succeeding stages.
		Mass extinctions of marine groups took place as a result of the drastic reduction in area and quality of habitat when extensive epicontinental seas regressed because of a fall in the sea level.
		Sole’s conclusion was that extinction process was self-similar fluctuation and a nonlinear response of the biosphere to perturbations provides the main mechanism for the distribution of extinction events.
	people.hnl.bcm.tmc.edu /cuixu/School/periodicity_in_extinction.htm (3276 words)

	Amazon.com: Extinction: Bad Genes or Bad Luck?: Books: David M. Raup (Site not responding. Last check: 2007-10-19)
		He also concluded that "wanton extinction" - selective extinction where some kinds of organisms survive preferentially but NOT because they are better adapted to their normal environment - was the primary ingredient in producing the kinds of results we see in the fossil record.
		The author's main thesis is that extinction is a mostly random event; due to catastrophes and bad luck, and not related to the process of evolution that is part and parcel of the Darwinian idea.
		Extinction is most often caused by new stresses that the organism is not accustomed to.
	www.amazon.com /Extinction-Bad-Genes-Luck/dp/0393309274 (2336 words)

	SPACE.com -- Theory: Mass Extinction by Our Own Sun
		ATLANTA (AP) - The second-largest extinction in the Earth's history, the killing of two-thirds of all species, may have been caused by ultraviolet radiation from the Sun after gamma rays destroyed the Earth's ozone layer.
		All this happened some 440 million years ago and led to what is known as the Ordovician extinction, the second most severe of the planet's five great periods of extinction.
		The extinction "could have been a one-two punch,'' said Bruce S. Lieberman, a paleontologist at the University of Kansas and a co-author of the theory.
	www.space.com /scienceastronomy/solar_extinction_040108.html (839 words)

	The Great Mystery: Background
		The "great dying," as it is sometimes called, is an example of a mass extinction: an episode in evolutionary history where more than 50% of all known species living at that time went extinct in a short period of time (less than 2 million years or so).
		The largest would be the "Permo-Triassic" extinction, between the Permian and Triassic periods, of the Paleozoic and Mesozoic eras.
		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)

	Atmospheric Optics Glossary
		EnchantedLearning.com's astronomy glossary is not bad, and is suited to schoolchildren.
		Extinction is the sum of actual absorption, and scattering.
		GREEN RIM: When the Sun is low, normal atmospheric dispersion raises the short-wavelength images of the Sun more than the long-wavelength images; but atmospheric extinction attenuates the blue so much that the upper edge usually appears green, not blue or violet.
	mintaka.sdsu.edu /GF/glossary.html (2861 words)

	Spaceflight Now \| Breaking News \| Report: Biggest extinction not from asteroid or comet
		The extinction occurred at the boundary between the Permian and Triassic periods at a time when all land was concentrated in a supercontinent called Pangea.
		"The marine extinction and the land extinction appear to be simultaneous, based on the geochemical evidence we found," said UW paleontologist Peter Ward, lead author of the paper.
		They found two patterns, one showing gradual extinction over about 10 million years leading up to the boundary between the Permian and Triassic periods, and the other for a sharp increase in extinction rate at the boundary that then lasted another 5 million years.
	www.spaceflightnow.com /news/n0501/22extinction (1178 words)

	Oread Researchers dress up mass extinction on 'Naked Science'
		One of the three biggest mass extinctions of life on Earth occurred about 440 million years ago, at the end of the Ordovician era, when most of the Earth was under water.
		Adrian Melott, professor of physics and astronomy; Bruce Lieberman, associate professor of geology; and Mikhail Medvedev, associate professor of physics and astronomy, have teamed up to develop a theory that a gamma-ray burst caused the mass extinction at the end of that period.
		Melott and Medvedev studied the coincidence of mass extinctions occurring when the sun oscillates to the north side of the galaxy.
	www.oread.ku.edu /2006/november/6/extinction.shtml (640 words)

	NASA - Explosions in Space May Have Initiated Ancient Extinction on Earth
		Scientists at NASA and the University of Kansas say that a mass extinction on Earth hundreds of millions of years ago could have been triggered by a star explosion called a gamma-ray burst.
		This research, supported by a NASA Astrobiology grant, represents a thorough analysis of the "mass extinction" hypothesis first announced by members of this science team in September 2003.
		Though there is no direct evidence, scientists say a nearby gamma-ray burst may have caused the great extinction of the late Ordovician period 450 million years ago, which killed 60 percent of all marine invertebrates.
	www.nasa.gov /vision/universe/starsgalaxies/gammaray_extinction.html (1155 words)

	Ebb and Flow of Life Itself Linked to Space
		One of the latest in these investigations is a mass extinction which took place about 380 million years ago and wiped out over forty percent of marine animals.
		This extinction may well be connected with an apparent impact which took place in the Moroccan desert.
		Another mass extinction being looked at is one which occurred 250 million years ago and may be related to the rise of the dinosaurs.
	starryskies.com /articles/2003/06/extinctions.html (650 words)

	96.06.03: Asteroids, Comets, and Meterorites: Their Intimate Relation with Life on Earth
		Of the major mass extinctions, there is strong evidence of extraterrestrial causes for two of these sudden interruptions in the history of life.
		The first persuasive evidence for an extraterrestrial cause for the K-T extinctions came with the 1980 discovery of a one centimeter layer of clay (initially found in northern Italy, and subsequently in nearly 100 sites around the globe) containing iridium, a platinum-group metal which is extremely rare in Earth’s crust but comparatively abundant in meteorites.
		The iridium is believed to have been laid down by the impact of a 10 km diameter asteroid, the resultant formation of a global dust cloud from the impact, and settling to Earth’s surface of the iridium carried in by the asteroid.
	www.yale.edu /ynhti/curriculum/units/1996/6/96.06.03.x.html (10429 words)

	GGI-H Comet Storm A'Coming - Astronomy.com Forums
		It is interesting to note that the number of extinction's is related, five in the 300Ma through 500Ma, as compared to two or three in the last 220M.
		But I think Blanc has missed some extinction, however his article needs updating, as his model of the Galaxy is not correct to present mappings.
		It's about the possiblity that mass extinctions are tied to the passage of the solar system through giant clouds in the galactic arms.
	www.astronomy.com /ASY/CS/forums/281241/ShowPost.aspx (6101 words)

	Internal extinction of spiral galaxies in the NIR (Site not responding. Last check: 2007-10-19)
		The question of how much extinction there is present in external galaxies at first glance does not appear to be the most interesting of topics.
		Even in the history of Astronomy it has played an important role - for example the first estimation of the size of our own Galaxy was seriously underestimated by Kapetyn because he did not take into account the role of interstellar extinction.
		Since edge-on galaxies are the ones in which extinction effects will be the largest, this means that determining an accurate extinction law is very important.
	www.astro.cornell.edu /~masters/NIRextinction.html (404 words)

	Astronomy Notes
		Astronomy as a Science and a Sense of Scale.
		I introduce astronomy's place in science, and give a sense of the size and time scales involved.
		Astronomy constants, physical constants, planets (orbital properties, physical characteristics, atmospheres), 100 nearest stars, and 100 brightest stars as seen from the Earth.
	www.astronomynotes.com (1161 words)

	Evolution: Extinction: A Modern Mass Extinction?
		Some Web visitors wrote to say they have heard it said, especially of tropical and marine organisms, that we are losing species before we even know of them.
		If extinction and mass extinctions are a natural part of Earth's history, should we really be concerned about our effects on endangered species?
		He has conducted extensive research on the rates and causes of species extinction, on the nature of ecological communities, and on the impacts and management of introduced species (those who migrate to a new area).
	www.pbs.org /wgbh/evolution/extinction/massext/bios.html (646 words)

	ThinkQuest : Library : Astronomy
		The educational objectives of "Astronomy for Kids" are to teach kids in grades 4 through 6 about astronomy and outer space in a fun and interesting manner.
		Astronomy, from the past to the present is covered at this excellent web site.
		Astronomy is the study of the stars, planets, and other objects in space.
	www.thinkquest.org /library/cat_show.html?cat_id=40 (4008 words)

	Astronomy
		Most professional positions in astronomy and astrophysics generally require study leading to the Ph.D. degree.
		Program of study for major: The Bachelor of Science degree requires a minimum of 48 credit hours in astronomy and physics courses in a program to be developed by the student and the advisor and approved by the department.
		Study of a selected field in astronomy, according to student's interests, such as practical astronomy, astrophysics, binary stars, celestial mechanics, etc. Prereq.: Consent of instructor.
	www.drake.edu /artsci/physics/Physics_and_Astronomy_Catalog.htm (2326 words)

	LiveScience.com - New Recipe: How to Make a Mass Extinction
		The most famous of all giant space rocks is the one that presumably killed off the non-avian dinosaurs 65 million years ago, in the so-called K-T extinction event.
		The P-T extinction event, or Great Dying, occurred 251 million years ago when up to 90 percent of all species were snuffed out.
		Arens and her colleagues analyzed geologic data from the last 488 million years and found more species died out when the environment was first stressed and then stung.
	www.livescience.com /environment/061027_mass_extinction.html (678 words)

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