The stable nitrogen- and carbon-isotope ratios of bone collagen are extremely important sources of dietary information about ancient populations. They provide quantitative estimates of individual diets and have therefore provided remarkable insights into dietary variation both between and within ancient human populations. However, they cannot be applied to charred or burned bones because it is known that the isotopic ratios change upon heating at temperatures higher than 150oC. This is a serious limitation because many cultures, such as those of the European Bronze Age and ancient Rome, cremated their dead, leaving only burned bones. And for certain types of very old sites, such as early hominid ones, carbonized bones are the only type of bone preserved, and are thus not usable with current technologies. Cooked animal bones, which could provide information about diet, also cannot be used at present. Preliminary laboratory data reveal a relation between the change of isotopic ratios of charred bone and a property (the g-value) of the electron spin resonance (ESR) spectrum from stable free radicals that are produced in the collagen by charring. With NSF support, an interdisciplinary team of an archaeologist and a chemist will be assisted by anthropology and chemistry undergraduates to further quantify this relationship and critically evaluate its applicability to archaeological problems. By comparing the isotope ratios and ESR g-values of laboratory specimens and prehistoric bones from two unusual sites in eastern North America, we will assess the whether it is possible to use ESR spectra to reconstruct the original isotope ratios of burned bones. The Klunk and Yokem sites in the lower Illinois Valley, USA have produced cremated and uncremated burials from populations whose isotopic ecologies are well known. In many cases, the burials were only partially cremated, leaving burned and unburned bones, and frequently even bones that show a charring gradient, so that is possible to sample burned and unburned portions of a single bone. The sites provide an opportunity to investigate the effects of diagenetic (chemical) changes on burned bones after burial from periods between 1,000 and 6,000 years ago. We will thus be able to assess the effects of burial time and conditions on the reconstructions. If ESR spectra could be used to reconstruct unheated isotope ratios, it would open up entirely new areas where stable isotope analysis could be applied to the reconstruction of prehistoric diet. In addition, the control samples will provide information useful to forensic scientists who need to reconstruct the thermal histories of victims of fires or explosions. The project will involve eight undergraduate students in an inter-disciplinary research team combining archaeology and chemistry.
