It's a dizzyingly busy time for scientists searching for life on distant planets. To date, astronomers have cataloged more than 6,000 planets beyond our solar system and are searching the atmospheres of the most promising worlds for chemicals that might be byproducts of life. Astrobiologists are particularly interested in atmospheres like Earth's that trap enough heat to support liquid water on the planet's surface, which scientists consider the key factor in determining whether a planet can support life as we know it.
But scientists also want to distinguish between "habitable" and "inhabited" worlds. To do that, they need to know what sorts of atmospheric conditions on a planet can be explained without life, so that they can identify planets with atmospheres that can only be explained by life's influence.
To provide that planetary baseline, University of Washington researchers built a complex virtual Earth with one crucial tweak: no life.
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