when a low pressure of CO2 (0.34 MPa at 25°C) was used in place of 6 MPa of CO2, the 7-day experiment at 200°C under otherwise identical condition led to the formation of methanethiol at a yield of 1.7% (based on H2S) with CO (3.2 μmol) and CH4 (1.1 μmol). Thus, as long as MoS2 is available, methanethiol synthesis is feasible in aquatic environments rich in H2 and H2S. This reaction may partially account for the sedimentary organosulfur compounds detected on Mars .