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Published on Aug 25, 2014
Up to 3 times in the past 2.4 billion years, Earth has become a desolate "snowball" with average global temperatures less than -70 degrees Fahrenheit. Only a runaway greenhouse process created by volcanic activity has saved the planet from an icy fate. | For more How the Universe Works, visit http://science.discovery.com/tv-shows...
Catch all new episodes of HOW THE UNIVERSE WORKS Wednesdays at 9/8c on Science Channel!