Organic carbon concentrations in 3.5-billion-year-old lacustrine mudstones of Mars.

The Sample Analysis at Mars instrument stepped combustion experiment on a Yellowknife Bay mudstone at Gale crater, Mars revealed the presence of organic carbon of Martian and meteoritic origins. The combustion experiment was designed to access refractory organic carbon in Mars surface sediments by heating samples in the presence of oxygen to combust carbon to CO2. Four steps were performed, two at low temperatures (less than 550°C) and two at high temperatures (up to 870°C). More than 950 mug C/g was released at low temperatures (with an isotopic composition of delta13C = +1.5 ± 3.8) representing a minimum of 431 mug C/g indigenous organic and inorganic Martian carbon components. Above 550°C, 273 ± 30 mug C/g was evolved as CO2 and CO (with estimated delta13C = -32.9 to -10.1 for organic carbon). The source of high temperature organic carbon cannot be definitively confirmed by isotopic composition, which is consistent with macromolecular organic carbon of igneous origin, meteoritic infall, or diagenetically altered biomass, or a combination of these. If from allochthonous deposition, organic carbon could have supported both prebiotic organic chemistry and heterotrophic metabolism at Gale crater, Mars, at 3.5 Ga.