Isotopic Reconstructions of Prehistoric Diet from Burnt Bones

稳定的骨胶原氮和碳同位素比值是古代人群饮食信息的重要来源。它们提供了个体饮食的定量估计，因此对古代人类种群之间和内部的饮食变化提供了非凡的见解。然而，它们不能用于烧焦或烧焦的骨头，因为已知同位素比例在高于150摄氏度的温度下加热时会发生变化。这是一个严重的限制，因为许多文化，如欧洲青铜时代和古罗马，将死者火化，只留下烧焦的骨头。对于某些非常古老的遗址，比如早期的原始人遗址，碳化的骨头是唯一保存下来的骨头，因此不能用目前的技术来使用。煮熟的动物骨头可以提供饮食信息，但目前还不能使用。初步的实验室数据揭示了烧焦骨头的同位素比率的变化与胶原蛋白中稳定自由基产生的电子自旋共振（ESR）谱的性质（g值）之间的关系。在美国国家科学基金会的支持下，一个由考古学家和化学家组成的跨学科小组将在人类学和化学本科生的协助下进一步量化这种关系，并批判性地评估其对考古问题的适用性。通过比较来自北美东部两个不寻常遗址的实验室标本和史前骨骼的同位素比率和ESR g值，我们将评估是否有可能使用ESR光谱重建燃烧骨骼的原始同位素比率。在美国伊利诺斯河谷下游的Klunk和Yokem遗址，已经发现了已知同位素生态的人群的火葬和非火葬。在许多情况下，埋葬只是部分火化，留下烧焦和未烧焦的骨头，甚至经常出现烧焦梯度的骨头，因此有可能对单个骨头的烧焦和未烧焦部分进行取样。这些遗址提供了一个机会来研究1000到6000年前埋葬后烧焦的骨头的成岩（化学）变化的影响。因此，我们将能够评估埋葬时间和条件对重建的影响。如果ESR光谱可以用来重建未加热的同位素比率，它将开辟一个全新的领域，稳定同位素分析可以应用于史前饮食的重建。此外，控制样本将为法医科学家提供有用的信息，他们需要重建火灾或爆炸受害者的热历史。该项目将由8名本科生组成一个跨学科研究小组，将考古学和化学结合起来。

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.