The preservation of amino acids within the calcite matrix of eggshells of the African Ostrich (Struthio camelus), has been shown to approximate a closed system. Indigenous proteinaceous materials are bound within the calcite crystals and there is essentially no loss of amino acids due to leaching or diffusion despite a steady degradation of high molecular weight polypeptide material to low molecular weight peptides and free amino acids. Because of this closed system behavior, the natural variability of specific degradation reactions in samples of known age is far less that in other carbonate systems; additionally, the kinetics of amino acid racemization are much simpler to model than in more open systems such as molluscan and foraminiferal fossils. Consequently, the potential for precise age, and/or paleotemperature calculations from the extent of these reactions is superior for the eggshell compared to all other media studies to date. Hominid lineages have a long history of interaction with ostriches. The ostrich egg, weighing between one and two kilograms, has been utilized as a food source by hominids for more that two million years. It is found commonly in association with hominid artifacts in the lowest strata at Olduvai Gorge, and in older beds elsewhere in Tanzania. By the end of the Middle Stone Age humans were also using the eggshell as a source material for decorative items such as beads, and ostrich eggshell fragments are commonly found in association with occupation levels at sites across Africa, the Near East, and Asia, where the ostrich has only recently become extinct. The ubiquitous occurrence of ostrich eggshell in hominid sites, especially in stratified sites, offers the potential of utilizing the remarkably straight forward time-dependent characteristics of amino acid racemization in the eggshell as a means of dating occupation levels beyond the range of radiocarbon. The principal investigators will conduct an analytical program that will focus on developing a more precise model of racemization kinetics in the eggshells of ostrich and other avian genera, including the modeling of decomposition reactions that hold the promise of extending the dating potential back into the Pliocene. They will apply the racemization reaction in ostrich eggshell to address questions related to the earliest appearance of anatomically modern humans in Africa, the emergence of specialized human cultures, and the migration of Homo sapiens sapiens across the Near East and Asia. They will also extend the eggshell research into Europe and Australia by utilizing the common occurrence of owl eggshell in the former, and emu eggshell in the latter area. Improved chronologies in these areas are relevant to questions related to persistence of isolated populations of Homo erectus and the colonization of Australia and Europe, including the possible interactions between different species, or subspecies, of the genus Homo.
