Could Life Have Started on Mars? Planetary Conditions That Assemble and Destroy Protocells

Early Mars was likely habitable, but could life actually have started there? While cellular life emerged from prebiotic chemistry through a pre-Darwinian selection process relevant to both Earth and Mars, each planet posed unique selection ‘hurdles’ to this process. We focus on drivers of selection in prebiotic chemistry generic to Earth-like worlds and specific to Mars, such as an iron-rich surface. Iron, calcium, and magnesium cations are abundant in hydrothermal settings on Earth and Mars, a promising environment for an origin of life. We investigated the impact of cations on the stability and disruption of different primitive cell membranes under different pH conditions. The relative destabilizing effect of cations on membranes observed in this study is Ca2+ > Fe2+ > Mg2+. Cation concentrations in Earth systems today are too low to disrupt primitive membranes, but on Mars concentrations could have been elevated enough to disrupt membranes during surface dehydration. Membranes and RNA interact during dehydration–rehydration cycles to mutually stabilize each other in cation-rich solutions, and optimal membrane composition can be ‘selected’ by environmental factors such as pH and cation concentrations. We introduce an approach that considers how life may have evolved differently under the Martian planetary conditions and selective pressures.