A Possible Route to K+-Enriched Aqueous Solutions on Early Earth

All known living organisms have a K+-rich intercellular medium, while usually existing in a Na+-enriched environment. High K+ concentrations are required for the proper function of numerous essential enzymes and ribozymes. This difference between cation concentrations is translated to potential difference used for energy storage and signalling. Most of the natural terrestral envinroments are known to be enriched in Na+ due to its higher abundance and high solubility of its salts. The Na+/K+ mole ratio inside living cells varies around 1/10, which is roughtly the opposite ratio of these ions in seawater (47/1). In this work we show that one of the processes leading to the enrichment of groundwaters in K+ can occur during acid weathering of Aluminium-rich clays and zeolites and the fractional secondary precipitation of alunite and Na-alunite Zeolites and montmorillonites were treated by acidic (0.1- 1M H2SO4) solutions (K+/Na+ mole ratio 1/5) at temperatures 20°-50°C. The clay/acid mixtures were left to evaporate. During the drying process octagonal crystals were formed from coalescent brines on the surface of the clays. The crystals were identified by X-ray diffraction and ICP analysis as KAl(SO4)2 The remaining interstitial brine was enriched in Na+ and close to saturation with respect to NaAl(SO4)2. Fast washing from the final mixture surface leads to the enrichment of K+ in the formed solution by orders of magnitude depending on pH, temperature and a mineral type. This proposed scenario leads to environments rich in potassium and can also be applied for accumulation of other prebiotic components, such as phosphate and small organic molecules. We suggest that acid weathering could be a process to accumulate essential components for the chemical origin of life.