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Credit: David A. Aguilar (CfA)
March 9, 2016
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Artist's rendering alien planet
Credit: David A. Aguilar (CfA)

Earth's early atmosphere of nitrogen, methane and carbon dioxide was hostile to life as we know it, but friendly to the first methane-loving bacteria. Astronomers modeled the history of the Earth's atmosphere to learn what fingerprints to seek on alien worlds.