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Anonymous
http://www.earth-policy.org/Updates/Update35.htm THE SIXTH GREAT EXTINCTION: A Status Report
Janet Larsen
Almost 440 million years ago, some 85 percent of marine animal species were wiped out in the earth's first known mass extinction. Roughly 367 million years ago, once again many species of fish and 70 percent of marine invertebrates perished in a major extinction event. Then about 245 million years ago, up to 95 percent of all animalsnearly the entire animal kingdomwere lost in what is thought to be the worst extinction in history.
Some 208 million years ago, another mass extinction took a toll primarily on sea creatures, but also some land animals. And 65 million years ago, three quarters of all speciesincluding the dinosaurswere eliminated.
Among the possible causes of these mass extinctions are volcanic eruptions, meteorites colliding with the earth, and a changing climate. After each extinction, it took upwards of 10 million years for biological richness to recover. Yet once a species is gone, it is gone forever.
The consensus among biologists is that we now are moving toward another mass extinction that could rival the past big five. This potential sixth great extinction is unique in that it is caused largely by the activities of a single species. It is the first mass extinction that humans will witness firsthandand not just as innocent bystanders.
While scientists are not sure how many species inhabit the planet today, their estimates top 10 million. Yet each year thousands of species, ranging from the smallest microorganisms to larger mammals, are lost for good. Some disappear even before we know of their existence.
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