Synchronising Radiocarbon Dating and the Egyptian Historical Chronology by Improved Sample Selection
Dee, M. W., Rowland, J. M., Higham, T. F. G., Shortland, A. J., Brock, F., Harris, S. A., Ramsey, C. Bronk, Antiquity
Literary sources from the Dynastic period of ancient Egypt provide the framework for anchoring chronology in the eastern Mediterranean throughout the Bronze Age. A network of linkages and synchronisms based on similarities in material culture radiate out from Egypt across the region. Such connections are fundamental to the early historical chronologies of north-east Africa, the Aegean and the Near East. For several decades, however, discrepancies between the Egyptian historical chronology and radiocarbon dating have been a source of controversy in the region, most famously in relation to the Minoan eruption of Thera (Friedrich et al. 2006; Bietak & Hoflmayer 2007; Manning 2007; Bruins 2010). For the last five years, our team has explored the possible reasons for such discrepancies. Our findings suggest that the primary cause was sample selection, both in the past and in our own research. It has become apparent that selecting radiocarbon samples for Dynastic Egypt is particularly challenging and requires an awareness of a number of different scientific and archaeological factors. Here, we explore the nature of this complexity and explain why some materials have previously produced inaccurate results. All of the most common materials sampled for radiocarbon dating are discussed. The patterns uncovered in our own data were also evident in a database of published radiocarbon results that we have collated and made available online (the Egyptian Radiocarbon Database, henceforward ERD). Our conclusions point the way forward for the proper application of the radiocarbon method to Egypt and the wider region.
Egyptian chronology played a key role in the development of radiocarbon dating. The first 'known-age' samples used by Libby to verify his method came from Egyptian archaeological contexts (see Arnold & Libby 1949). Unfortunately, however, recurrent discrepancies between radiocarbon and historical dates have dented confidence in the accuracy of the method in Egypt. Some high-profile examples include the radiocarbon dates obtained for Khufu's funerary boat (Stuckenrath & Ralph 1965, c. 600-700 years older than expected) and wood from the tomb of Tutankhamun (Nakhla & Mohammed 1974, c. 200-300 years older than expected). In a substantial recent project, Bonani et al. (2001) made 269 radiocarbon measurements on Egyptian samples. The data set showed marked variability, and once more revealed significant offsets from historical dates to both younger and older ages. For example, the measurements made on the Great Pyramid were approximately 50-300 calendar years older than historical estimates. Importantly, the Bonani et al. (2001) study suggested that contamination derived from museums or laboratories could not be the primary reason for such offsets, as the samples were all obtained from freshly excavated sites and the analyses conducted at three different laboratories. Our team, at the University of Oxford and Cranfield University, also recently completed a study of Dynastic Egypt. Its central objective was to determine the reason for the offsets by obtaining a new set of radiocarbon samples on short-lived materials that were unimpeachably well contextualised. It was intended that every sample be associated with the reign of a specific pharaoh, thereby allowing us to compare radiocarbon measurements directly with historical dates. In order to achieve the highest levels of precision possible, the dates were modelled using Bayesian statistical techniques.
Before analysing the archaeological samples, we first investigated whether an environmental process could have affected the accuracy of radiocarbon dating in Egypt. This involved measuring 75 plant samples of known calendar age collected in Egypt during the eighteenth and nineteenth centuries AD. Crucially, these plants grew prior to the construction of the first Aswan dam, which began in 1899. …