Formation of prebiochemical compounds in models of the primitive earth's atmosphere. II: CH4 - H2S atmospheres.

In order to understand the role of sulfur in the primitive atmosphere, we have studied the action of a silent discharge on mixtures of CH4 and H2S at low pressure. The nature of the products formed in the gaseous phase, and the influence of several parameters, especially the H2S percentage, on the yield of the products are reported. The analysis of the products is carried out by gas liquid chromatography and infrared spectrometry. The formation of sulfur-containing compounds, such as thiols and sulfides, is reported. CS2 is formed in high yield (a few percent) in mixtures containing 40-50% of H2S, while the maximum concentration of thiols (i.e., CH3SH and C2H5SH) is reached with lower percentages of H2S. The formation of hydrocarbons decreases rapidly with increasing proportions of H2S. These results show the important inhibitor effect of H2S on the formation of hydrocarbons and the possibility of occurrence of many sulfur compounds in prebiological evolution.