Getting our teeth into the Quaternary: analytical methods for amino acids in enamel

Tracking the protein breakdown in a closed-system is a powerful technique for dating fossils1 and analysis of intra-crystalline amino acids in carbonate shells has led to the most comprehensive dating framework for the British Quaternary (the last 2.6 Ma). However it is the direct dating of animals (e.g. mammals) that remains a key challenge in geology and archaeology. This project aims to build on the pilot results we have on dating enamel, testing the methods of extraction, the patterns of degradation, and its application to fossils.
The extent of protein degradation (and particularly amino acid racemization, AAR) in fossils can be used to assess relative age over time spans beyond the reach of radiocarbon dating (~50,000 years), a time period particularly difficult to date. Our breakthrough has been to isolate proteins entrapped within biominerals, which therefore behave as a closed system2, apparently neither losing products nor gaining reactants over periods in excess of 30 million years. The combination of this closed-system approach with advances in chromatography, allowing the analysis of the concentration and extent of racemisation of multiple amino acids, provides an extremely powerful dating tool.
The earliest attempts to date teeth using amino acids used dentine, but enamel shows considerable promise for closed-system behaviour3. However, analysis of enamel is not straightforward, as the phosphate mineral interferes with the chromatographic separation. Removal of the phosphate is not facile, as any extraction protocol must not affect the amino acids, as this will skew the results. Pilot work on solid phase extraction, ion exchange and filtration methods have yielded some promising results and this project will further explore the possible routes forward. A series of chemical extraction methods will be tested exhaustively using modern and artificially aged enamel samples, tracking the breakdown patterns of the enamel proteins through high temperature experiments. In collaboration with the Natural History Museum, we will test the application of the analytical protocols on the excellent stratified sequence of the British Quaternary. The student will sample tooth enamel from a range of large mammal fossils (e.g. mammoths and woolly rhinos), many of which will be directly-relatable to AAR in mollusc shells. If successful, the technique would be expanded to other species and geographic areas, and could become an important method for dating Quaternary fauna.
The project offers an enviable range of multidisciplinary training; the student will gain hands-on expertise in state-of-the-art techniques for analytical method development and amino acid racemisation (chiral amino acid analysis by RP-HPLC and UHPLC), as well as working with a team which will bring experience of fieldwork and sampling approaches. The preparative and analytical techniques will be a great strength in any field of chemistry. Due to the inter-disciplinary nature of this research, the Chemistry student will be fully supported by the project team in the archaeological, geological and geochemical background and interpretation, with additional training available through exciting opportunities to go into the field for sample collection. The excellent opportunities of public outreach possible through the Natural History Museum will also be exploited

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