Least destructive rapid scanning of human teeth to test their suitability for U-series analysis

Abstract

Excavations in the Grotte de la Chèvre have taken place since the 19th century and yielded more than 100 human specimens together with numerous artifacts from the Middle Paleolithic, Upper Paleolithic, and more recent times. Unfortunately, due to considerably different excavation standards in earlier excavations, none of the specimens can be securely provenienced. Some of the remains may represent oldest humans fossils found in historic Brittany. This can only be confirmed through direct dating. On faunal materials, U-series dating is usually carried out a series of analyses along a cross-section profile, which necessitates the cutting of the specimen. Here, we present a rapid scanning method, which allows the assessment of whether a sample is actually suited for U-series dating with minimal sample damage. Laser ablation ICP-MS was used for the analysis of U-series isotopes close to the surface of the roots of two teeth from the Grotte de la Chèvre. The laser analysis created pits with a diameter of about 200µm and a depth of about 100µm. This allowed the assessment of the 230Th concentrations close to the surface of the dentine where the oldest apparent U-series ages are expected. In the first sample, all isotopic concentrations were too low for the calculation of meaningful U-series results, while the second sample yielded very low 230Th/238U activity ratios, indicating a recent age of perhaps a few thousand years. Consequently, both teeth did not require any further destruction. Rapid scanning can be applied to a large number of samples to identify those which will most likely yield reasonable age estimations, leading to informed decisions about geochronological sampling strategies, including radiocarbon. We envisage that laser ablation spot analyses also could be used to obtain U-series depth profiles, which are required for open system dating, as well as depth profiles for other isotopes (e.g., Sr, Pb) to gain insights into prehistoric human migrations.