The Curiosity rover observed high Mn abundances (>25wt % MnO) in fracture-filling materials that crosscut sandstones in the Kimberley region of Gale crater, Mars. The correlation between Mn and trace metal abundances plus the lack of correlation between Mn and elements such as S, Cl, and C, reveals that these deposits are Mn oxides rather than evaporites or other salts. On Earth, environments that concentrate Mn and deposit Mn minerals require water and highly oxidizing conditions; hence, these findings suggest that similar processes occurred on Mars. Based on the strong association between Mn-oxide deposition and evolving atmospheric dioxygen levels on Earth, the presence of these Mn phases on Mars suggests that there was more abundant molecular oxygen within the atmosphere and some groundwaters of ancient Mars than in the present day
We gratefully acknowledge the very helpful comments of M. Osterloo and N. Tosca. This research was carried out in the U.S. under contract from NASA's Mars Program Office. Work in France was carried out with funding from the Centre National d'Etude Spatiale and in Canada by the Canadian Space Agency. This team acknowledges the Jet Propulsion Laboratory for developing and leading the Mars Science Laboratory (MSL) Curiosity rover mission. The data reported in this paper are archived at the Planetary Data System, accessible at http://pds‐geosciences.wustl.edu/missions/msl/index.htm. Additional data are available as supporting information.