As mentioned earlier, Mars got its reddish hue due to the oxidation of iron contained in its rocks and soil. It was that oxidation process that eventually robbed Mars of its oxygen, according to Wood. Water that was present on the surface of early Mars also disappeared as a reaction with the rocks. “So, water is consumed, carbon dioxide is to some extent consumed and the oxygen is consumed by reaction between oceans and atmospheres and the rocks,” said Wood.
A view of the surface of Mars taken at the "Intrepid" crater by the Opportunity Mars Rover on November 11, 2010. (NASA/JPL-Caltech/Cornell University)