Carboniferous and Permian periods

Carboniferous and Permian periods - Carboniferous and...

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Carboniferous and Permian periods Introduction Extinction, by definition, is when a species or any taxon of organisms disappears and it’s important to recognize that we can refer to either a single species or any taxonomic level. Genera, Families even Orders, any of the taxonomic levels have the potential to become extinct. The real problem is pinpointing when it occurs because by definition it happens when the last of the taxon disappears. As a species nears extinction it becomes very rare either living or in a fossil form and that makes the last one very hard to find in order to pin point the date for the extinction. It’s the reason why you may see stories in the news about an organism that was thought to be extinct is found in some very remote part of the planet. It’s a bit easier with the fossil record because we see organisms from the distant past that are clearly not alive on the planet now. But when they actually disappeared isn’t always clear. Yet extinction is a fairly common event and the best estimates are that 99% of the living organisms on the planet have gone extinct. As one species evolves and the branching pattern progresses early forms are replaced and become extinct. As habitat changes species may be lost as others adapt. New predators may destroy a prey species, or a disease may appear that destroys a group of organisms. The shifting continents may also cause certain groups to flourish while others are destroyed. All of this is the background level of extinction that is always occurring. But there are also some instances when the numbers that disappear in extinction event are large. If its 50% of the taxa disappears it’s considered a mass extinction. There have been five of these in the history of the planet and biologists believe that we are currently in the middle of the sixth mass extinction – one that we have created ourselves. The estimate is that 50% of the species on the planet will disappear by 2100 in what is now known as the Holocene mass extinction. Background and mass extinctions Although the idea of mass extinctions is an attention grabbing idea it’s are only one of two types of extinction that occur, the other being background extinctions. The name is a reference to a continuous background rate of extinction that occurs on the planet. Evidence from the fossil record suggests that most species survive for about 10 million years before they eventually disappear. The rate varies and while invertebrates seem to survive for 11 million years marine vertebrates seem to live for only 5 million years before being replaced with a new species. The extinction rate for mammals is only a million years. Even with these differing rates what is clear is that more species have been lost in earth’s history to background extinctions than to mass extinctions.
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A mass extinction is when 50% of the genera (Genus level) are lost and most often the marine environment is where measurements are made. A reason for this is that the marine
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This note was uploaded on 12/03/2011 for the course SCIENCE BIO1130 taught by Professor Fenwick during the Spring '11 term at University of Ottawa.

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Carboniferous and Permian periods - Carboniferous and...

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