The structures and compositions of modern and fossil charcoal samples were compared in order to evaluate charcoal degradation processes in archaeological sites. Modern charcoal samples produced in campfires contain two major phases: graphite-like microcrystallites and a non-organized phase. These phases create a mosaic-like structure with differing relative proportions depending on the taxonomic source of the wood used. Fossil charcoal samples (Tel Dor, Israel: 3000 years BP and Kebara Cave, Israel: 40,000 years BP) also contained the graphite-like microcrystallites and the non-organized phases, but were clearly altered compared to modern charcoal. The graphite-like phase of the fossil charcoal has much higher electrical resistivity, and its ESR properties show that it has markedly altered surface electronic states. Infrared spectra show the presence of additional carboxylate groups. Oxidation has therefore altered the structure. This appears to be a "self-humification" process that affects the graphitic component, and probably the non-organized phase as well.
Bibliographical noteFunding Information:
We thank Talmon Arad for his expert help with the TEM. We also thank Ofer Bar-Yosef for his help with the Kebara Cave samples, Dan Namdar for the samples from Ohalo II, Amihai Mazar for the Tel Rehov samples, Hamudy Khalaily for the Motza samples and Ilan Sharon and Ayelet Gilboa for the Tel Dor samples. We thank Mr. George Schwartzmann, Sarasota, Florida, for his generous support. We also thank the Kimmel Center for Archaeological Science for their financial support. S.W. is the incumbent of the Dr. Trude Burchardt professorial chair of Structural Biology.
- Graphite-like microcrystallites
- Humic acid
- Radiocarbon datings