Nearly 4 billion years ago, much of the surface of Mars was like a soppy carpet. The planet was covered by a thick atmosphere, and it was warm but not exactly picturesque. Those conditions, an international team of three dozen scientists has concluded, could have supported primitive forms of life. However, over time — some 800 million years — Mars dried up and took on the rocky, desert-like appearance that exists today. The scientists’ findings are based on mineralogy data collected by the Reconnaissance Orbiter, a U.S. spacecraft that has circled the Red Planet since March 2006.
