This line of research is focused on the direct dating of fossil remains found in archaeo-paleontological context, with special emphasis on those that cannot be dated using Radiocarbon, either because showing unsuitable characteristics or simply because beyond the limits of the method. In particular, there is an increasing need in Modern Archaeology and Palaeoanthropology to develop reliable dating tools in order to provide direct chronological constraints to fossils older than 50 ka. This line of research combines methodological investigations as well as dating application studies in geo-archaeological contexts.
Direct dating offers the advantage of minimizing the inherent uncertainty originating from the correlation of different layers or from the association of the host sediment with archaeo-palaeontological evidence, which is sometimes either unclear or can only provide minimum and/or maximum age brackets for the fossils due to stratigraphic constraints.
This line of research mainly employs two dating methods: U-series, used either alone or in combination with Electron Spin Resonance (ESR). Both methods can be routinely applied not only to fossil bones and teeth from large mammals, but also to highly valuable fossil remains. In the first case, the standard procedure is based on solution U-series analyses in combination with ESR measurements of powdered enamel, while dating human fossils require a more advanced protocol employing high resolution Laser Ablation (LA) U-series analyses with ESR measurements of enamel fragments. The second approach, more complex and time consuming, has the advantage to minimize the damage caused to the fossils, a major challenge when dating such invaluable samples.
Dating applications, using either the standard or more advanced procedures, are focused on fossils bones and teeth from archaeo-paleontological sites located on various continents and covering the whole (Early, Middle and Late) Pleistocene time range: Europe (e.g., Orce, Atapuerca, Bolomor, Cueva Negra), Asia (e.g., Khok Sung, Ngalau Sampit; Ngalau Gupin), Arabia (e.g., Nefud Desert), Israel (e.g,. Mislyia), Oceania (e.g., Lake Callabonna; Chichilla) and Africa (e.g. Gona, Ain Boucherit).
In particular, in the last 5 years, several key human fossil specimens have been directly dated, such as Homo naledi, a possible ancestor of Homo florensiensis at Mata Menge, the oldest Homo sapiens found outside Africa, Homo antecessor from Atapuerca Gran Dolina, or the phalanx of Homo sapiens from Al Wusta (Saudi Arabia).
Methodological developments are essential to improve the reliability, accuracy and standardisation of the numerical dating methods. They include, among others:
- The development of a pre-screening procedure to differentiate suitable from non-suitable fossil teeth for ESR dating. This procedure is based on the use of high LA ICP-MS U-series analyses of dental tissues in order to rapidly identify any occurrence of uranium leaching or high uranium concentration values, which typically preclude the application of the ESR method.
- The quantification of the impact of micro-CT scanning on ESR dating of fossils. This analytical technique has become extremely popular in palaeoanthropology because it is supposed to be non-destructive and provides key information about the internal structure of teeth. However, micro-CT scanning is a real issue for ESR dating, as it is based on the X-rays irradiation of fossils. A specific procedure has been developed to accurately assess the X-rays dose absorbed by the fossil during micro-CT scanning analysis.
- Cross-comparisons with other independent numerical dating methods providing either direct (e.g., C-14) or indirect (OSL, Palaeomagnetism, Cosmogenic Radionuclides) age constraints to the fossils