Pleistocene geochronology and palaeothermometry from protein diagenesis in ostrich eggshells: implications for the evolution of modern humans

Proteinaceous residues incorporated within the crystal structure of ostrich eggshells (OES) are retained without loss over geological time exceeding 10 million years. Degradation of the polypeptides, including hydrolysis of smaller peptide fragments and eventual release of free amino acids, decomposition, and racemization and epimerization occur at regular, predictable rates dependent on ambient temperature. The extent of isoleucine epimerization (aIle/Ile ratio) in OES follows linear first-order reversible kinetics in controlled-temperature laboratory simulations of time up to an aIle/Ile ratio in excess of 1.0. The hydrolysis of leucine also follows a predictable pattern, but deviates from first-order kinetics. A non-linear mathematical model has been developed that adequately describes the pattern of leucine hydrolysis through a wide temperature range. The ages of levels at Border Cave, South Africa, from which anatomically modern human skeletal remains have been recovered, are dated by the extent of isoleucine epimerization in associated OES. -from Authors