The Case of the Lacking Carbonates and the Emergence of Early Life on Mars

The mineralogical characterization of Mars by different exploration missions, provides a new image of the earliest conditions that prevailed on the planet surface. The detection of extensive deposits of phyllosillicates has been considered to be as a result of the production of hydrated silicates through alteration and precipitation under neutral to sub-alkaline conditions. Although extensive deposits of carbonates should precipitate beneath a thick CO2-bearing atmosphere, only a few outcrops of Mg-rich carbonates have been detected on Mars. Paradoxically those carbonates occur in association with geological units exposed to acidic paleoenvironments. Given such geochemical conditions on Earth, the carbon cycle is intimately associated with life, then, we can assume that the presence or absence of microbial communities should have impacted the distribution of those carbonate compounds on Mars. In this paper, we suggest three potential geobiological scenarios to explain how the emergence of life on Mars would have impacted the carbon cycle and, hence, the formation of carbonates on a planetary scale.