Sunday, 5 August 2018

Using strontium isotope analysis to identify the origins of cremated human remains from Stonehenge.

Stonehenge is an internationally renowned Neolithic monument located on Salisbury Plain in Wiltshire, southern England, thought to have been constructed between 4000 and 5000 years ago.. The monument comprises a ring of standing stones, each of which is about 4 m high and 2.1 m wide, and weighs about 25 tonnes, known as the Sarsen Stones, thought to be derived from Marlborough Downs, about 30 km away, within which is a ring of smaller stones, the Blue Stones, which have been identified as having been sourced from Mynydd Preseli (Preseli Hill) in Pembrokeshire, west Wales, around 240 km away. The site has been the subject of numerous archaeological excavations, and, between 1919 and 1926, a total of 58 sets of cremated Human remains were found within the complex, within a series of pits known as 'Aubry Holes' after the seventeenth century antiquarian John Aubrey who first noted them.


In a paper published in the journal Scientific Reports on 2 August 2018, Christophe Snoeck of the School of Archaeology at the University of Oxford, and Analytical, Environmental & Geo-Chemistry at the Vrije Universiteit Brussel, John Pouncett, also of the School of Archaeology at the University of Oxford, Philippe Claeys and Steven Goderis, also of Analytical, Environmental & Geo-Chemistry at the Vrije Universiteit Brussel, Nadine Mattielli of the G-Time Laboratory at the Université Libre de Bruxelles, Mike Parker Pearson and Christie Willis of the Institute of Archaeology at University College London, Antoine Zazzo of the Unité Mixte de Recherche ‘Archéozoologie, Archéobotanique: Sociétés, Pratiques et Environnements’ at the Sorbonne Universités, and Julia Lee-Thorp and Rick Schultin, again of the School of Archaeology at the University of Oxford, describe the results of a study which uses strontium isotope analysis to attempt to uncover the geographical origin of the cremated remains.

Strontium isotopes in water vary with local geology, and are incorporated in tooth and bone, providing a record of where people have lived. Strontium isotope levels in tooth enamel become fixed at about puberty, reflecting the isotopic content of the water consumed at this time, unlike bone where the isotope content varies with water consumed throughout the life of the individual, and are often used not just in archaeology but in the identification of modern remains by forensic scientists, in those working with war graves and similar sites. 

However, the strontium signature of tooth enamel is almost invariably destroyed by cremation, which causes the enamel to shatter and break down. As an alternative, Snoeck et al. extracted strontium isotopes from bone fragments that have survived cremation. The strontium isotope ratio in bone does not become fixed at puberty as it does in tooth enamel, but continues to change over the lifetime of the individual, but it does provide an average reading of the foods eaten over the last decade or so before death, giving some idea where that individual was living.

Cremated occipital bone fragments from Stonehenge. Snoeck et al. (2018).

Snoeck et al. carried out analyses on bone fragments from 25 individuals, and compared them to the isotope ratios of the chalk geology of the Salisbury Plain,as well as plant samples from eight locations in West Wales, and previously published modern plant, water and dentine data from around Britain.

Fifteen of the tested individuals produced results consistent with having lived and died in the region around Stonehenge, however the remaining ten were clearly not local, and had strontium isotope ratios consistent with having lived in Devon, West Wales, or some more distant location outside the study set (such as Ireland, Scotland or continental Europe).

Biologically available strontium (BASr) baseline (left – mean and right – 1 SD), generated using the Spatial Join and Polygon to Raster tools in ArcGIS Desktop 10.6. Based upon British Geological Survey map Geology 625k.

Snoek et al. also not that the ratio of carbon isotopes in the local and non-local individuals was different. Carbon isotope ratios from bone or tooth enamel are generally assumed to represent the diet of an individual rather than where they lived, and since there is thought to have been little variation in the diet of Neolithic peoples across Britain, might be expected to be similar in all of the Stonehenge individuals. 

However, the carbon isotope ratios of cremated remains are known to be reset by the cremation process, with bone fragments absorbing carbon from the wood used in the cremation process. Carbon ratios in wood reflect the environment in which the tree which produced the wood was living, with wood produced by trees from open woodland distinct from wood from trees from more densely wooded environments. During the time when Stonehenge was constructed southern England, including Salisbury Plain and Devon, is thought to have been only lightly wooded, while the west of Wales is reconstructed as having been covered by dense woodland. This suggests that the non-local individuals found at Stonehenge both lived and were cremated in West Wales, with their remains being later transported to the site to be buried.

See also...

http://sciencythoughts.blogspot.com/2016/08/identifying-cloths-of-otzi-iceman.htmlhttp://sciencythoughts.blogspot.com/2016/08/determining-diets-of-late-mesolithic.html
http://sciencythoughts.blogspot.com/2016/01/animal-remains-from-middle-neolithic.htmlhttp://sciencythoughts.blogspot.com/2014/08/the-first-dairy-farmers-in-finland.html
http://sciencythoughts.blogspot.com/2014/06/does-catalhoyuk-mural-depict-volcanic.htmlhttp://sciencythoughts.blogspot.com/2014/04/a-palliative-dental-filling-from.html
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