It has been a long and contentious debate over whether Mars was warm and wet or cold and icy early in its history. Large Hesperian-aged (~3.7 Ga) layered deposits of sulfate-rich sediments in the equatorial regions have been attributed to playa-like evaporative environments created under prolonged warm conditions. Paul Niles and his colleagues studied the weathering of olivine by cryo-concentration of acidic solutions in the laboratory to simulate formation processes of hydrated sulfates on Mars under a cold and icy environment. Their results indicate that olivine can be rapidly chemically weathered to form sulfates by cryo-concentrated acidic brines even at temperatures as low as -60 ºC. Together with other evidence, they argue that sulfate formation under a cold and icy environmental condition on Mars is not only possible, but unavoidable. READ MORE »