Speculation about the existence of other life in the universe has become invigorated in recent decades by an explosion in the discovery of extrasolar planets.  The numbers tell the story. There were about 50 known exoplanets in year 2000, about 500 known by 2010, and we're approaching 5,000 today.  Powerful telescopes can reveal information about the chemical composition of the atmospheres of these far away planets.  Can they also tell us if there is life there?  They could if the atmospheres of planets with biospheres differed systematically from the atmospheres of lifeless planets, Knowing that, however, would require knowing what the atmosphere of a lifeless planet looks like, and how life might change it. This grant funds an effort led by Anan Shahar at the Carnegie Institution for Science to determine the abiotic atmospheric baseline of the most common planets in our galaxy, sub-Neptune and rocky planets. With the abiotic baseline known, scientists can then consider how Earth-like life might change a planet's atmosphere and in this way tackle the question of whether or not it's possible to determine signatures of life by studying exoplanet atmospheres The research team will pursue an interdisciplinary, holistic approach that combines solid-planet expertise with atmospheric expertise in order to understand the baseline abiotic atmosphere of a planet and how it evolves over the planetary lifecycle.  What’s called a planet’s primary atmosphere is formed early in a planet’s  formation, as the planet coalesces from matter orbiting a local star.  This atmosphere then evolves into a secondary atmosphere, one shaped both by geologic processes on the planet itself (volcanism, magma oceans, outgassing, the weathering of the planet’s surface) and by external forces like comet impacts.  The research team will attempt to model and the analyze the effects of these forces, shedding light on how the atmospheres on lifeless planets are likely to evolve across the planetary lifecycle.