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extinction
extinction
extinction 1. In optical mineralogy, a
mineral is said to be in extinction when the
vibration direction of the two rays of a doubly refracting
crystal coincide with the vibration directions of the two pieces of
Polaroid in a thin-section microscope that is parallel to the
polarizer and
analyser so that no light reaches the eye. This phenomenon occurs four times in a complete 360° rotation of the stage. See
OBLIQUE EXTINCTION;
STRAIGHT EXTINCTION;
SYMMETRICAL EXTINCTION; and
UNDULOSE EXTINCTION.
2. The elimination of a
taxon. This may take place in several ways. In the simplest case the taxon disappears from the record and is not replaced. Alternatively, one taxon may replace another, the earlier group consequently disappearing. Thus there is a process of either subtraction or substitution. Extinction generally takes place at particular times and places but there are recurring periods when episodes of mass extinction have taken place. Environmental catastrophe, occurring for whatever reason, removes many groups from the environment and ecosystems collapse. Eventually new forms appear and evolution resumes. It would appear that periods of mass extinction control the pattern of evolution.
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Extinction: Bad Genes or Bad Luck?
Magazine article from: BioScience; 5/1/1992; ; 700+ words
; ...during mass extinctions, only to...after the extinction of a dominant...mechanism for all extinction events. Raup...even all, extinctions of the geological...processes in extinction, particularly in mass extinctions. Other paleontologists...
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Mass extinctions and macroevolution
Magazine article from: Paleobiology; 1/1/2005; ; 700+ words
; ...between later background extinction and the major mass extinctions. In any case, the...the intervals of lower extinction intensity between the "Big Five" extinction peaks of the Phanerozoic). Mass extinctions would thus represent...
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Extinction-induced variability in human behavior.(Report)
Magazine article from: The Psychological Record; 6/22/2009; ; 700+ words
; ...be changed by reinforcement and be a product of extinction. Under extinction, responses that led to reinforcers in the past...on the reinforcement of variability, but while extinction-induced variability appears essential for the...
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Spacing extinction trials alleviates renewal and spontaneous recovery
Magazine article from: Learning & Behavior; 2/1/2009; ; 700+ words
; Studies of extinction in classical conditioning situations...varying the intertrial interval during an extinction treatment in a fear-conditioning...at test (i.e., more effective extinction) when extinction trials were widely...
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EXTINCTION sunday briefing sunday briefing While the disappearance of species such as tigers and mountain gorillas grabs the headlines and fills TV schedules, less well-known is the fact that we appear to be living through an extinction event bigger than that which wiped out the dinosaurs. This assault on biodiversity is seen by many scientists as a greater threat to mankind than climate change.
Newspaper article from: The Sunday Herald; 12/10/2006; 700+ words
; ...YEARS AGO A series of mass extinctions eliminated many brachiopods...pictured below). These extinctions could have been caused by...444 MILLION YEARS AGO Two extinction events occurred, which together...largest of the five major extinctions in history in terms of the...
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Mass Extinctions: Processes and Evidence.
Magazine article from: BioScience; 7/1/1990; ; 700+ words
; ...papers on mass extinctions in geochronological...different mass extinction. To these are...identity of mass extinctions (S. K. Donovan...associated with extinction events (C. J...underlying the extinction events they describe...aspects of mass extinctions is that they appear...
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Extinction and quiescence in marine animal genera
Magazine article from: Paleobiology; 4/1/2007; ; 700+ words
; ...proxies for true extinctions, then there is appreciable global extinction in every stage...backsmearing of extinctions by incomplete...to which mass extinctions represent something...aggravated background extinction (Jablonski 1986...
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Evidence for extinction selectivity throughout the marine invertebrate fossil record
Magazine article from: Paleobiology; 10/1/2009; ; 700+ words
; ...this nonrandom extinction is selective clustering of extinctions in genera consisting...species which possess extinction-biasing traits...debated whether mass extinctions form a distinct...background" extinction (Bambach et al...
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Extinction Rates.
Magazine article from: BioScience; 3/1/1997; ; 700+ words
; ...on current extinction rates by evaluating past extinctions using the...human-caused extinctions eliminates...number of extinction-resistant...prehistoric extinctions - particularly...relatively extinction-resistant...
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Extinction cascades and catastrophe in ancient food webs
Magazine article from: Paleobiology; 1/1/2006; ; 700+ words
; ...catastrophic secondary extinction increases as food...of the secondary extinctions. When intraguild...understanding secondary extinctions in fossil communities...during times of mass extinction, within the context...results in the extinction of consumers...such secondary extinctions ...
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Extinction
Encyclopedia entry from: The Gale Encyclopedia of Science
...greatest burst of extinctions in at least...million years. Extinction as such is...exceptional mass-extinction events, each...major mass extinctions, and about...average rate of extinctions in the time...accelerate extinction: falling...
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extinctions and mass extinctions
Book article from: The Oxford Companion to the Earth
extinctions and mass extinctions Extinction of species is a continuous process, and evidence...result in the development of new species. Mass extinctions are events during which the rate of extinction rises dramatically above this background rate...
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Mass Extinction
Encyclopedia entry from: The Gale Encyclopedia of Science
...what can be called the background extinction rate, the extinctions that are always occurring at a normal...large “ normal ” extinction becomes suddenly a mass extinction. Mass extinctions are characterized by the loss of...
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mass extinction
Book article from: The Columbia Encyclopedia, Sixth Edition
...most recent mass extinction was that of the...associated with mass extinctions. Theories regarding...for the Permian extinctions include the effects...final Cretaceous extinction is that one or...final Cretaceous extinction is that it resulted...and Cretaceous extinctions), ...
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extinction
Book article from: A Dictionary of Earth Sciences
extinction 1. In optical mineralogy, a mineral is said to be in extinction when the vibration direction of the two rays of...360° rotation of the stage. See OBLIQUE EXTINCTION ; STRAIGHT EXTINCTION ; SYMMETRICAL EXTINCTION...
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