Silica-carbonate biomorphs of alkaline earth metals: Relationship with minerals since the Precambrian era

Under alkaline conditions, silica forms self-assembled mineral compounds which are similar in morphology, nanostructure, and texture to the hybrid biomineral structures that, millions of years ago gave to life. In this review we propose that, during the earliest history of this planet, there was a geochemical scenario that led to large-scale production of both simple and complex organic compounds, many of which were important for prebiotic chemistry. The production was based on a high concentration of silica and high pH. Two main factors affected this process: a) a source of simple carbon molecules that were either synthesized abiotically from reactions associated with serpentinization, or carried by meteorites and produced by their impact on Earth, and b) the formation of self-organized silica-metal mineral compounds that catalyzed the condensation of single molecules in a reduced methane-rich atmosphere. We discuss the plausibility of this geochemical scenario and its catalytic properties and the transition towards a slightly alkaline to Neutral Ocean.