Mineral surfaces probably participated in the chemical processes which led to life in the primitive oceans. The ordered conformations of simple acidic peptides exposed to insoluble minerals are described. Alternating poly(Glu-Leu) adopts a random coil conformation in water due to charge repulsion. The polypeptide extracts cations from insoluble crystalline CdS or molybdenum and adopts an ordered conformation. CdS leads to the formation of beta-sheets whereas molybdenum leads to alpha-helices. Peptides with at least 10-amino acids are necessary to exhibit a significative adsorption onto the surface. Under the same conditions, montmorillonite adsorbs the polypeptide but does not induce any conformational change.