PerspectivePlanetary Science

Carbonates and Martian Climate

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Science  23 Jul 2010:
Vol. 329, Issue 5990, pp. 400-401
DOI: 10.1126/science.1192828

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The case for global climate change on Mars is neither ambiguous nor arguable. Cold, dry, and dusty right now, the surface of Mars shows ancient fluvial valley networks, catastrophic flood channels, sediment-filled basins, and many other features that require stable liquid water at the planet's surface. Such observations from orbit (1) imply that ancient Mars was substantially warmer than it is today. The favored scenario to heat up a young Mars is greenhouse warming driven by a thick, primitive CO2-rich atmosphere of the kind thought common to all the terrestrial planets (2). Clearly, the greenhouse phase didn't last long for Mars. As a result, almost every model for martian climate history includes an appreciable drawdown of CO2 by precipitation of carbonates. However, only a small fraction of the carbonates predicted by this theory have been detected. On page 421 of this issue, Morris et al. (3) report the detection of ample carbonates dispersed within the subsurface, thereby strengthening arguments that CO2 played a major role in the early martian climate system.