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Exoplanet oxygen may not signal alien life

Water and ultraviolet light could create the gas without help from organisms

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11:24am, March 18, 2014

The first sign of extraterrestrial life probably won’t be a spaceship landing in a cornfield or a radio transmission from deep space. Most likely, the announcement will be encoded in the chemistry of a distant planet’s atmosphere. On Earth, oxygen betrays life’s presence. But oxygen in an exoplanet’s atmosphere wouldn’t necessarily point to alien shrubbery. Two researchers argue that an ocean-bearing planet zapped by its sun’s ultraviolet light could masquerade as a living world.

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