Phosphate Solubility and the Cyanate-Mediated Synthesis of Pyrophosphate

The justification for a less alkaline primordial ocean (than present) is briefly reviewed, along with constraints on aqueous phosphate under such conditions. Based on the assumption that CaHPO4 dihydrate determined the availability of phosphorus species, we have carried out laboratory simulations to determine equilibrium concentrations as a function of pH (in PIPES buffer) with added NaCl and CaCl2. Consistent with expectations, solubility declines with higher pH and [CaCl2], but increases only slightly with [NaCl]. Significantly, PIPES shows no specific effect on the dissolution beyond its influence on pH and ionic strength. Data are also presented on the synthesis of pyrophosphate from the NaOCN/CaHPO4·2H2O system, which could have provided a source of this phosphate anhydride on the early Earth.