Ten Things That Cause Mass Extinctions

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From Cosmos:

SYDNEY: It's normal for a species to go extinct, and an average rate of one a year is the natural background rate. But over the past 4.5 billion years, there have been times when extinctions occured at 100 to 1,000 times faster - with the largest event wiping out 95 % of all species. Somewhere between five and 20 such mass extinctions have occured. Here are 10 possible causes for future extinction events.

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