Changes in the mineral characteristics of montmorillonite (Mt) resulting from exposure to sodium sulfide (Na2S) or artificial seawater revealed the capacity for clays to absorb and protect amino acids or nucleic acids from hydrolysis or UV radiation on the prebiotic Earth. The pH of isoelectric point (pHiep) of the modified montmorillonite (MMt) increased probably due to the adsorption of Na+ from the solution of Na2S, and would likely enhance the adsorption of biomolecules that are not protonated at higher pH. However, the exchange of cations with Na+ from artificial seawater or Na2S solutions likely contributed to the observed decrease in the interlayer distance of all treated samples. The associated release of Fe3 + from treated Mt likely decreased the capacity for the clay to adsorb biomolecules. The amount of Fe2 + in solution decreased by almost 50% when Mt was mixed with artificial seawater, but this decrease was not observed when Mt exposed to Na2S and artificial seawater. Given the capacity for Fe2 + to react with nucleic acids, this protection could be important for establishing chemical environments on the prebiotic Earth.