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Marine Amino Acid Racemisation Investigation of the Mediterranean

Final Report Summary - MAARITIME (Marine Amino Acid Racemisation Investigation of the Mediterranean)

mAARiTIME (marine Amino Acid Racemisation dating of the Mediterranean Rim) is a highly-interdisciplinary project that brought together the fields of Archaeology, Quaternary Sciences, Biology, Geochronology and Chemistry. Through protein geochronology (amino acid racemisation dating, AAR), it set out to answer two specific but vital questions: when did early humans become “modern”, and is “modern” behaviour isolated to our own species? Behavioural modernity has fortuitously left traces in the archaeological record as molluscan remains, one of the best substrates for AAR dating. Molluscs were exploited as a food resource and shell used as personal ornaments, providing some of the earliest evidence of symbolic thinking displayed by early humans. These appear between 160-70 ka ago, a period which falls tantalising outside that of many commonly-applied dating techniques.

mAARiTIME investigated the potential of a new methodology of AAR geochronology (intra-crystalline protein diagenesis, IcPD) to date molluscan remains from archaeological and geological sites spanning the Mid-to-Upper Pleistocene and Holocene around the Mediterranean rim, which is a key area to the development of behavioural modernity. Our main aim was to test whether IcPD could be used effectively in this new environment, and to select the best substrate (or a range of substrates) that could be used, by isolating a closed system of proteins from a range of molluscan taxa (e.g. Patella, Osilinus/Phorcus, Glycymeris, Pecten and others) commonly found in the area. This included the investigation of the mechanisms of protein diagenesis as well as the spatial localisation of the intracrystalline proteins within the shell’s ultrastructure. The second aim was to target well-dated sequences and build a calibrated chronological framework of AAR for the Mediterranean record for the last 200 ka (and beyond), incorporating sites at different latitudes and longitudes, allowing us to assess the effect of temperature on the extent of degradation. Finally, we aimed to use the newly-established geochronological frameworks to improve the dating of geological/archaeological sites in the Mediterranean, including those that are key for understanding development and evolution of early modern humans, e.g. the Haua Fteah Cave in Libya.

We achieved the main objectives of the project: we undertook one of the largest-scale investigation of protein breakdown mechanisms in mollusc shells (8 different taxa) by applying state-of-the-art chiral amino acid, proteomic and imaging techniques; we built site-specific chronological frameworks and assessed the time-depth and resolution for each taxon. The work carried out within the mAARiTIME framework provides an exceptionally strong foundation for future geochronological investigations of the area, that can be conducted on the basis of this robust reference dataset. New substrates for intra-crystalline AAR dating have been identified (e.g. the shells Osilinus/Phorcus, Pecten, Littorina, Patella), whilst molluscan taxa that had been used traditionally in the area (e.g. Glycymeris) have been shown to be less suitable for IcPD dating. Cchronological frameworks, calibrated with other independent dating techniques have been developed for a range of sites in Italy, northern Africa, Spain and Greece, showing that reliable age information can be obtained at least back to ~400 ka (e.g. on Pecten from the well-dated raised beach sequences of the Gulf of Corinth in Greece).

One of the key objectives of this project was to establish strong collaborative links with researchers across Europe and across disciplines: we have brought together geologists, archaeologists, geochronologists, environmental scientists, chemists, physicists and mathematicians from institutions in the UK, Italy, Spain, Gibraltar, Germany, Denmark and the US and set strong foundations for multi-disciplinary scholarly endeavours. Our work philosophy is strongly targeted towards effective knowledge transfer: we have trained, supervised and hosted students and peers from across the world and organised outreach activities aimed at school-age pupils and the general public, and we are striving to disseminate our research within and outside the scientific community.

The impact of this research is not confined to a single discipline, or indeed to a scientific audience only: not only we have set a benchmark and a reference framework for future AAR studies in the Mediterranean, but we have begun to unravel some of the complexities of protein breakdown patterns, with a wider impact than on geochronology and Quaternary sciences. For example, building on our growing understanding of diagenesis, we have started to investigate the effects of amino-acid specific racemization in living tissues, which is at the forefront of medical research in ageing. We have worked in close collaboration with biomineralisation scientists and are beginning to understand the complex relationship between amino acids and mineral skeleton in mollusc shells and how these may impact on the suitability of the organisms for AAR geochronology. We are developing a new approach, based on amino acid and protein signatures, for the species identification of worked shells (used as personal ornaments) that cannot be identified on the basis of morphology; this has already caught the interest of museum conservators and curators, as it would enable a range of archaeological hypotheses on trade and exchange patterns to be tested, or indeed may help to identify whether endangered taxa are traded (illegally?) today.

Overall, this project represents a successful example of integration between research fields, crossing boundaries between disciplines and nations, and we hope it will be an important stepping stone in further strengthening the links between northern and southern Europe in this area of research.