Enrichment of Potassium During Simulated Weathering of Chloride Evaporites

This paper reports a simple, prebiotically feasible process
for
the enrichment of potassium salts from the seepage of water through
evaporated mixtures of chlorides thought to dominate Earth’s
early ocean. When water passes through a mixture of NaCl and KCl,
the solid dissolves and the initial eluate contains NaCl:KCl in a
2.4:1 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 eluate transitions to a saturated solution of the remaining
salt. If the initial mixture of salts contains <2.4:1 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. For
this quinary system, the eluate initially contains NaCl:KCl:MgCl2:CaCl2 in an approximate ratio of 1:1.6:4:4. CaCl2 and MgCl2 are depleted rapidly relative to NaCl
and KCl, and once the calcium and magnesium are exhausted, 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 collectively demonstrate a potential
mechanism for the enrichment of potassium salts that could have transpired
naturally on the Prebiotic Earth to generate the sort of potassium-rich
environment that may have fostered early life on the planet.