Our Ancestors Survived 'Snowball Earth'

It has been 2.3 billion years since Earth's atmosphere became infused with enough oxygen to support life as we know it. About the same time, the planet became encased in ice that some scientists speculate was more than a half-mile deep. That raises questions about whether complex life could have existed before "Snowball Earth" and survived, or if it first evolved when the snowball began to melt.

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<p><a href="http://www.physorg.com/news68814293.html">Our Ancestors Survived 'Snowball Earth'</a></p> <p>It has been 2.3 billion years since Earth's atmosphere became infused with enough oxygen to support life as we know it. About the same time, the planet became encased in ice that some scientists speculate was more than a half-mile deep. That raises questions about whether complex life could have existed before "Snowball Earth" and survived, or if it first evolved when the snowball began to melt.</p>