Transport Dynamics Across Prebiotic Hydrothermal Mineral Barriers: Comparison with Contemporary Proton Motive Pathways

Extant life relies on phospholipid membranes that selectively manage the flux of materials from one side to another. Prior to the development of such complex organic membranes, the separation of life from nonlife, or inside from outside, may have been achieved by geological inorganic barriers. Submarine alkaline hydrothermal vents, with their inherent pH gradients across inorganic mineral structures and a steady supply of H2 and CO2, are considered plausible environments for the transition from geochemistry to biochemistry. Analogous to extant life, which harnesses proton gradients for CO2 reduction, these vents may have facilitated early carbon fixation through electrochemical processes mediated by Fe(Ni)S minerals. To investigate the potential bottlenecks in such prebiotic scenarios, we electrochemically characterized the electron and ion conductivity of synthetic FeS, Fe(Ni)S, and Green Rust under aqueous conditions mimicking a hydrothermal vent interface, using electrochemical impedance spectroscopy (EIS). Our results reveal that these minerals exhibit substantial electronic conductivity (1.5 x 10-2 - 3.6 x 10-2 S/cm) and moderate ionic conductivity (1.01x10-6 – 6.22x10-5 S/cm). Contemporary phospholipid membranes, by contrast, allow significant ion passage but are electrically insulating. These findings provide insights into the physicochemical properties of hydrothermal vent minerals and their potential role in facilitating early prebiotic reactions. Specifically, we introduce to the pH gradient hypothesis the concept of ion conductivity as a possible limiting factor on the flow of electrons needed for the production of organics across vent mineral barriers.