Photo: "Alien" Atmosphere Helped Unfreeze Early Earth



Part of a glacier extends across a dry valley in Antarctica in an undated photo.

Some experts believe early Earth reached a threshold that caused the entire planet to stay covered in ice and snow. A January 2009 study says rocks from the Arctic are offering proof of an otherworldy atmosphere rich in carbon dioxide that might have helped melt millions of years' worth of deep freeze.

Photograph by George F. Mobley/NGS


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