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Developing High Resolution Electron Spin Resonance (ESR) dating of fossil teeth: contribution to the chronology of early hominid occupations in the Mediterranean area

Final Report Summary - HR_ESR (Developing High Resolution Electron Spin Resonance (ESR) dating of fossil teeth: contribution to the chronology of early hominid occupations in the Mediterranean area)

• Summary description of the project objectives
Electron Spin Resonance (ESR) is one of the very few numerical dating methods that can be applied to fossil remains beyond the Radiocarbon time range. Recent investigations focused on Early-to-Middle Pleistocene samples have highlighted the limitations of the standard procedures, as well as the complexity of the post-depositional alteration processes in dental tissues at micro-scale. To overcome these issues, the present project proposes a cutting-edge investigation that can only be performed as a joint project between the Research School of Earth Sciences at the Australian National University (RSES, ANU, Australia) and the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH, Spain), since these institutions offer complementary expertise in terms of facilities and experienced staff.
Basically, the project aims are: (i) investigating the physical and chemical processes that are affecting dental tissues at micro-scale and evaluating their impact on the ESR age results, (ii) improving the reliability and accuracy of the ESR dating method by developing new procedures and approaches, and in particular high resolution combined US-ESR dating of fossil teeth, and (iii) complementing the existing chronological framework of the Palaeolithic dispersals across Africa, Asia and Europe, with a special emphasis on the Mediterranean area.

• Description of the work performed since the beginning of the project
During the two years of the project (Oct.2014-Sept.2016) at RSES and CENIEH, the investigation carried out by the Marie Curie Fellow has involved a large variety of activities including fieldwork, laboratory analyses, data reduction and interpretation, as well as dissemination.
Regarding fieldwork, several sampling sessions were organised at different key Paleolithic sites located in the Mediterranean area, such as La Solana del Zamborino, Alto de las Picarazas, Cueva Negra, Atapuerca Gran Dolina (Spain), and Mislyia cave (Israel). Laboratory work has been mostly focused on the understanding of the physical and chemical processes affecting the teeth over time by investigating: (i) the incorporation of Uranium into dental tissue by means of high resolution Laser Ablation ICP-MS U-series analyses, (ii) the reliability and accuracy of ESR dose evaluation through the development of new analytical procedures for ESR measurements of enamel powder and fragments. The amount of data produced lead to the development of specific data reduction procedures in order to extract useful information from all the analyses performed during the two year. The fellow had also attended several trainings courses/workshops in Bayesian and dose rate modeling, which are very powerful approaches that enable to build more robust chronologies.
Dissemination activities over the two years included, among others: (i) poster and oral presentations at several conferences in Australia, Spain, UK, France and Japan (8 first-author contributions and 17 co-author works), (ii) the publication of > 20 scientific papers (including 19 already accepted and 2 submitted; at least 6 are currently in preparation) in peer-review journals (e.g. PlosOne, Nature, Quaternary International, Journal of Human Evolution, Quaternary Geochronology, etc.), (iii) lectures given at University seminars (e.g. University of Newcastle, The Australian National University, University of Cologne), (iv) articles in popular science magazine (in French and Spanish); (v) Participation to the European Researchers’ Night 2016. Results from the investigation were also widely diffused through press releases towards national and international news agencies as well as social and dedicated media (e.g. Twitter, ResearchGate).
Finally, peer-review and editorial activities have also been a non-negligible part of the work carried out during the two years, with 17 manuscripts reviewed for international journals and two grant proposals NSF (US) and ANR (France) agencies, as well as the elaboration as a Guest Editor of two special volumes of Quaternary international and Geochronometria. The fellow also developed mentoring and training activities during the Return phase at CENIEH, through the supervision of a laboratory technician and three PhD students who were trained to the most advanced procedures in ESR dating.

• Achievements
The investigation carried out during the two years of the project have lead to some major achievements not only in terms of research outcomes but also regarding new competencies acquired/developed by the Marie Curie Fellow (MD). The project has indeed contributed to foster his scientific maturation. As an additional evidence of his increasing influence in the field of Quaternary Geochronology, MD has been recently invited to become member of the Editorial Board of the journal Quaternary Geochronology and is currently member of the Scientific Advisory Committee of the next Luminescence and ESR Dating 2017 meeting in Cape Town (South Africa).
Among the major methodological research outcomes, it should first be mentioned the development of new analytical procedures to ensure reliable dose estimations of fossil tooth enamel, one of the major challenges in ESR dating. The investigation has been focused on defining of the most appropriate conditions to ensure reliable fitting. This pioneering work has been validated by two peer-reviewed publications in Radiation Measurements (Duval, 2015) and Quaternary Geochronology (Duval and Grün, 2016). In addition to that, the first direct comparison between X-band and Q-band spectrometries has been published in PlosOne (Guilarte et al., 2016), demonstrating the potential – and the limitations – of the latter for dosimetric purpose. Much effort has also been dedicated to the development of original analytical and data reduction procedures for fossil enamel fragment measurements. This is especially useful to understand the nature and composition of the ESR signal of enamel, and for dating hominin remains that cannot be powdered. After his training at ANU during the Outgoing phase, MD implemented this procedure at CENIEH and tested it on several fossil humans (see later). Another important research question has been addressed as well through the thorough evaluation of the impact of CT-scanning onto ESR dating results, as this procedure is routinely applied to obtain 3D images of valuable hominin fossil remains (Duval and Martín-Francés, submitted). The high resolution LA-ICP-MS U-series analyses of several tens of Early-to-Middle Pleistocene fossil teeth from various sites and different sedimentary contexts (Spain, Israel, Algeria, Saudi Arabia, Indonesia, etc..) also enabled to define criteria to assess the potential of each sample for the use of the combined US-ESR dating: the implementation of a systematic pre-screening procedure helps to quickly identify and discard unsuitable samples that can simply not be dated. This is perfectly illustrated in the work by Stimpson et al (2016). Finally, the high resolution ESR dating approach has been tested on a series of fossil tooth samples by combining high resolution Laser Ablation ICP-MS U-series analyses and ESR microdosimetry. Results provide some crucial information regarding the variability of ESR and U-series data within a given tooth, as well as among different teeth (see example in fig. 1). The results obtained for Cuesta de la Bajada (Spain) were presented at the Q10 meeting in Bordeaux (see section Dissemination), and a paper is currently in preparation.
However, the investigation performed during this project has not only a strong methodological aspect, but also has an important dating application component. Dating results have been obtained for several key sites such as Misliya cave, which has provided evidence of modern human presence (Hershkowitz et al., submitted). Among other studies, it is worth mentioning the work done at Mata Menge that indicated that H. floresiensis most likely arrived much earlier than previously thought in the Flores island (Brumm et al., 2016). ESR results obtained at Ain Boucherit (Algeria) document the oldest occupation in Northern Africa, while the work performed at Atapuerca Gran Dolina and the Rising Star provides the first direct ages on H. antecessor and H. naledi remains (Duval et al., in prep.; Berger et al., in prep.). Those are a few exemples among other works that have been either already published or in preparation (see full detail in section Dissemination). Altogether, those dating results provide an important contribution to the understanding of early hominin dispersal across Europe, Africa and Asia during the Pleistocene.

• Expected final results and their potential impact
The study of our origins and especially of the early hominin migrations in the Mediterranean area (cf. the “Out-of-Africa” theory) has always been a major topic of investigation in the scientific community, as well as a source of great interest and fascination for the general public as attested by the increasing success of books or TV documentaries. This is why the results of this project are expected to attract widespread attention at national and international levels.
The investigation developed for this project has provided (and will provide) some major advances in Quaternary geochronology and Mediterranean Palaeolithic archaeology. The international significance of this study ensures that its impacts will extend far beyond the simple fact of dating several archaeological sites. The new ESR dating results have already significantly contributed to improve our knowledge of the Paleolithic settlements across Europe, Africa and Asia. From a methodological perspective, the project provides a major contribution to the fundamentals of ESR dating applied to fossil teeth, by developing a series of new approaches and procedures that contribute to improve the reliability of the ESR method through a better understanding of the physical and chemical processes that are affecting dental tissues at micro-scale. These developments are crucial, as ESR is actually the only chronometric method that can be applied to fossil remains whose age is beyond the radiocarbon time range. The importance of this investigation has been recently become reinforced by several major paleoanthropological discoveries (e.g. the identification of Homo naledi in South Africa, or the earliest evidence of modern human at Fuyan cave, China) for which ESR appears to be the only candidate to provide direct age constraints on the fossils. Some of the remaining unpublished results derived from this project will tentatively be published in open access in order to ensure their wider diffusion, in case funds for post-grant FP7 publications are granted through the Post-Grant Open Access Pilot initiative.

To cite this report:
Duval (2016). Developing High Resolution Electron Spin Resonance (ESR) dating of fossil teeth: contribution to the chronology of early hominid occupations in the Mediterranean area. FP7-MC-IOF project 626474 (HR_ESR). Final report.