Abstract A thermodynamical analysis of the multicomponent system SiTiAlFeMnMgCaNaKPCHO open with respect to CO 2, CO, H 2O was carried out. Hydration and carbonatization processes are proposed to be geochemical consequences of the hypothesis of quasi-equilibrium conditions between the troposphere and crustal surface rocks. The probable rock-forming hydrated mineral phases are represented by epidote, glaucophane, tremolite, phlogopite, and annite; the carbonatization results in existence of calcite and dolomite as rock-forming minerals of weathered alkaline lavas. The surface rocks are assumed to have high ferric/ferrous iron ratios. The wollastonite equilibrium is rejected as a buffering chemical reaction. Hydrated minerals could be stable at least up to 5-km depths and contribute about 0.1 × 10 24 g of H 2O whereas about (0.7–0.8) × 10 24 g of H 2O would be consumed in ferrous iron oxidation with concomitant hydrogen dissipation. The distribution of H 2O in the outer planetary shells is possibly a function of their temperatures.