Thermodynamics of heterogeneous iron—Carbon systems: Implications for the terrestrial primitive reducing atmosphere

Abstract

I consider the problem of the early-earth surface—atmosphere chemical environment in which initial biochemical synthesis occurred. The model of a strongly reducing atmosphere developed by Oparin, Miller and others is reviewed and reasons for doubting its validity given. As an alternative, I propose that the primary source of carbon for biochemical genesis on the early earth was CO 2 and the fundamental chemical process was reduction by ferrous ion in the primitive ocean, for which radiation was required as an initiator but not as a source of free energy. The formation of reduced C compounds, including the biologically important amino acids, is shown to be a thermodynamically spontaneous process in the heterogeneous system comprising CO 2 and N 2 at reasonable pressure in contact with Fe (II)-containing minerals likely to have been present in abundance on the early earth. Possible mechanisms for formation reactions are considered, and an early role for primitive ferredoxin-type redox catalysts is postulated. The suggested early-earth environment was similar to that apparently present on Mars, except for the absence of large permanent bodies of liquid water on the latter.