Mass Extinction, Prehistoric Facts — National Geographic

More than 90 percent of all organisms that have ever lived on Earth are extinct. As new species evolve to fit ever changing ecological niches, older species fade away. But the rate of extinction is far from constant. At least a handful of times in the last 500 million years, 50 to more than 90 percent of all species on Earth have disappeared in a geological blink of the eye.

Artwork by Peter Arnold, Inc./Alamy

~ by sternbo on January 5, 2011.

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