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Warmth in the dark age

Lower reflectivity kept Earth from freezing under a fainter young sun

1:00pm, March 31, 2010

Though the sun was so much dimmer billions of years ago that the young Earth should have been literally freezing, the planet remained largely covered with liquid water. That was thanks to a substantially darker surface and a dearth of light-scattering clouds, a new study suggests.

“All other things being equal, Earth should have been frozen over for the first half of its existence,” says James F. Kasting, a geoscientist at Pennsylvania State University in University Park who was not involved in the research. “But it wasn’t.”

Previously scientists have explained the presence of liquid water at that low-light time, during the Archean eon of geologic history, by suggesting that Earth’s atmosphere held large amounts of planet-warming greenhouse gases such as carbon dioxide and methane. But new analyses show that greenhouse gases weren’t dramatically higher then compared with today, a team of earth scientists reports in the April

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