This project reports a simple, prebiotically-feasible process for the separation of potassium salts from sodium salts, as is seen in living cells. When water passes through a mixture of NaCl and KCl, the solid dissolves and the initial eluant contains NaCl:KCl in a 2.5:1 molar ratio, consistent with the invariant point of the NaCl-KCl-H2O ternary system. The ratio of eluted NaCl:KCl remains constant until the supply of one of the salts in the solid phase is exhausted and the eluant transitions to a saturated solution of the remaining salt. If the initial mixture contains <2.5:1 NaCl:KCl, a pure solution of KCl will eventually elute from the system. Similar behavior extends to the weathering observed in NaCl-KCl-MgCl2-CaCl2-H2O mixtures. Upon weathering of this quinary system—which contains the ions thought to dominate the composition of the ancient prebiotic ocean—the calcium and magnesium are exhausted quickly and the system returns to the behavior observed of a NaCl-KCl-H2O ternary system. The universal enrichment of potassium ions by cells—driven by ion transporters and channels—suggests that potassium is critical to life as-we-know-it and was possibly a biochemical relic of the environment where life originated. The weathering experiments described here demonstrate a potential mechanism for the enrichment of potassium salts that could have transpired naturally on the Prebiotic Earth to generate potassium-rich environments that may have fostered early life on the planet.

The group would like to thank their faculty sponsor Paul Bracher for their support of this project.