Abstract: Behavior of atmophile elements in the early inner solar system will be discussed in the light of the S-rich and FeO-poor chemistry of Mercury recently revealed by the MESSENGER spacecraft. In order to explain such an anomalous chemistry, building stones of Mercury are required to be prepared in a reduced, high temperature environment with C/O ratio significantly larger than that of the solar composition. A likely mechanism for producing such a thermochemical environment in the innermost solar nebula is the inward migration and partial vaporization of dust containing refractory organics. This suggests that organics have been also incorporated in the solid materials that eventually accreted to the outer terrestrial planets. Because hydrogen and carbon delivered by organics are soluble to molten metal and silicate melt produced on an accreting planet, both elements are partitioned to the proto-atmosphere with significantly fractionated proportions relatively enriched in H2 and H2O. This explains the present volatile abundance pattern observed for the silicate Earth including the hydrosphere. A hydrogen-rich wet proto-atmosphere, favorable for prebiotic chemical evolution, would then gradually become oxidized through the hydrogen escape to space.