The Origin-of-Life Reactor and Reduction of CO2 by H2 in Inorganic Precipitates

It has been suggested that inorganic membranes were forerunners of organic membranes at the origin of life. Such membranes, interposed between alkaline fluid in submarine vents and the more acidic Hadean ocean, were thought to house inorganic molecular machines. H+ flowed down the pH gradient (Delta pH) from ocean to vent through the molecular machines to drive metabolic reactions for early life. A set of experiments was performed by Herschy et al. (J Mol Evol 79:213-227, 2014) who followed earlier work to construct inorganic precipitate membranes which, they argued, would be transected by a Delta pH. They supposed that inorganic molecular machines might assemble by chance in the precipitate membranes, and be capable of using the Delta pH to drive unfavourable reduction of CO2 by H-2 to formate and formaldehyde. Indeed, these workers detected both of these compounds in their origin-of-life reaction vessel and contend this was proof of principle for their hypothesis. However, it is shown here by a straightforward calculation that the formate produced was only that which reached on approach to equilibrium without any driving force from Delta pH. We conclude that the reaction was facilitated by isotropic catalysts in the precipitate membrane but not by an anisotropic Delta pH-driven molecular machine.