Redox Chemistry Of Early Earth And The Origin Of Life

Carbon-silicate cycle includes a carbon dioxide (CO2) dissolution in rainwater to form carbonic acid (H₂CO₃) that falls on land and oceans; b reaction of H₂CO₃ and silicate (SiO₃₂-) to form silicon dioxide (SiO₂) and carbonate (CO₃₂-), which is sequestered into oceanic crust for further recycling to the mantle followed by release into the atmosphere through volcanic activity; and c regeneration of CO₂ through reaction between SiO₂ and CO₃₂-. Carbon fixation includes (d) reduction of CO₂ to methane (CH₄) through (e) the production of H₂ from H₂O on the surface of iron sulfide minerals that serve as sources of dissolved ferrous ion (Fe₂+), which is photochemically oxidized to ferric ions (Fe₃+.) in water vapor. Carbon monoxide (CO) either reacts with (f) H₂O for synthesis of formic acid (HCOOH) or g ammonia (NH₃) for synthesis of formamide (HCONH₂). Hydrogen cyanide (HCN) formation may occur through either h reaction between CH₄ and NH₃ or i reaction of CH₃• and N• through free radical mechanism. j HCN further reacts with H₂O to produce CO and NH₃.that also is produced through (k) N₂ fixation under high temperatures, both can be sequestered into the mantle; l NH₃ photolysis by UV radiation gives rise to N₂ and H₂; m hydrothermal H₂ production occurs through the H₂O oxidation by Fe₂+ into H₂ used for N₂ fixation in the atmosphere. In this figure, royalty-free mountain and meteorite images designed by Freepik platform (www.freepik.com) are used. — Nature via PubMed (open access)