Pedogenic processes and the drying of Mars

What exactly caused Mars to lose its liquid water billions of years ago remains as one of the most enduring questions in planetary science. New insights from Mars suggest that crustal hydration – the formation of hydrated minerals during aqueous alteration of the crust – contributed to the long-term drying of the planet. Here, we advance the hypothesis that hydration of the Martian crust could have resulted in part from precipitation-driven surface weathering of mafic sediments, which on Earth leads to pedogenesis, i.e., the formation of soil. Over the past decade, features resembling buried soils have been detected in thousands of locations across the ancient surface of Mars. Although soil has been traditionally defined by its biological component, growing evidence of global scale soil formation on a presumably lifeless Mars suggests abiotic pedogenesis was a critical process early in the planet’s history. Here we argue that pedogenic processes could have consumed large amounts of Mars’ exchangeable liquid water via the formation of hydrated pedogenic minerals. Since there is no evidence of plate tectonics to liberate and recycle water from hydrated minerals on Mars, the global formation of soil billions of years ago could have contributed to the irreversible desiccation of the planet.