Evaporite Borate-Containing Mineral Ensembles Make Phosphate Available and Regiospecifically Phosphorylate Ribonucleosides: Borate as a Multifaceted Problem Solver in Prebiotic Chemistry

RNA is currently thought to have been the first biopolymer to support Darwinian natural selection on Earth. However, the phosphate esters in RNA and its precursors, and the many sites at which phosphorylation might occur in ribonucleosides under conditions that make it possible, challenge prebiotic chemists. Moreover, free inorganic phosphate may have been scarce on early Earth owing to its sequestration by calcium in the unreactive mineral hydroxyapatite. Herein, it is shown that these problems can be mitigated by a particular geological environment that contains borate, magnesium, sulfate, calcium, and phosphate in evaporite deposits. Actual geological environments, reproduced here, show that Mg2+ and borate sequester phosphate from calcium to form the mineral lüneburgite. Ribonucleosides stabilized by borate mobilize borate and phosphate from lüneburgite, and are then regiospecifically phosphorylated by the mineral. Thus, in addition to guiding carbohydrate pre‐metabolism, borate minerals in evaporite geoorganic contexts offer a solution to the phosphate problem in the “RNA first” model for the origins of life. It's RNAs’ world: Geological strata show that Ca2+ does not take phosphate to form prebiotically unreactive apatite if borate, SO42−, and Mg2+ are present. Rather, phosphate is sequestered in the mineral lüneburgite. Upon evaporation, lüneburgite converts ribonucleosides regiospecifically to their phosphates. Thus, borate solves many problems in the synthesis of prebiotic RNA.