Friend or foe? - Viennese chemists optimise analysis of bones found at 7,000-year-old battlefield

Precise determination of strontium in bone material now makes it possible to distinguish between friend and foe on neolithic battlefields. A team of researchers at the University of Natural Resources and Applied Life Sciences, Vienna, has succeeded in using this sophisticated method to analyse skeleton finds. The interdisciplinary project, supported by the Austrian Science Fund (FWF), has opened the way for fascinating reconstructions of prehistoric events.

Archaeological headache: precise analysis of the ratio of the strontium isotopes 87Sr und 86Sr in bones helped solve a prehistoric puzzle. © Use of this photo for editorial purposes is free of charge, subject to attribution: Maria Teschler-Nicola

Strontium (Sr) is a chemical element that builds up in the bones and tooth enamel as food is digested. In nature, Sr occurs in a variety of forms (isotopes) which differ according to the number of particles in the atomic nucleus. The 87Sr und 86Sr isotopes are important for the classification of bone material. The ratio between the two varies and changes over time in accordance with geological conditions. As the strontium in the bones is constantly exchanged with the Sr ingested with food, the isotope ratio in bone material reflects that in the surrounding area. Because of this the Sr isotope ratio provides clues about a person's origins. However measuring the ratio accurately is a challenging task. A team under Prof. Thomas Prohaska of the Institute of Chemistry at the University of Natural Resources and Applied Life Sciences has now succeeded in achieving hitherto unknown levels of accuracy with this form of analysis.

Explaining how the team solved the crucial problem of separating the Sr from rubidium which is chemically very similar, Prof. Prohaska said: "Rubidium naturally decays into 87Sr. To precisely quantify the 87Sr we must therefore be able to separate it from the rubidium. A chromatographic method, HPLC, enabled us to do this. The key to success was transferring the samples purified in this way directly to the instrument used to analyse the Sr - a plasma mass spectrometer."

Proof on the battlefield
The scientific usefulness of the method was demonstrated at an excavation in cooperation with a team under Prof. Maria Teschler-Nicola of the Vienna Museum of Natural History. More than 100 human skeletons have been found very close together at the site of a neolithic village in Asparn, Lower Austria. The archaeologists wanted to know what had happened there 7,000 years ago.

The question as to whether there had been fighting at the village could not be answered by traditional anthropological methods. These depend on comparisons of morphological characteristics, meaning that the skeletons need to be in an excellent state of preservation. Only when the results of anthropological research were complemented by determination of the Sr isotope ratio was it possible to identify a group of skeletons unambiguously as those of villagers who had been defeated by intruders.

More information from molars
Another FWF funded project is refining Prohaska's method. The work is aimed at determining the migratory behaviour of individuals. To this end the Sr Isotope ratio in the bones is compared with that in the molars. In contrast to the bones, Sr is no longer exchanged in tooth enamel after the age of four, so the isotope ratio remains identical with that prevailing where the person lived as a child. Hence different isotope ratios in the bones and teeth are proof of migration after the age of four.

This research project, which has been supported by the FWF for several years now, is an impressive example of the ways in which analytical chemistry, archaeology and anthropology can join forces to produce new insights. The results of the work are a convincing demonstration of the value of multidisciplinary research.

Contact
A.o. Univ.-Prof. Dr. DI. Thomas Prohaska
Institute of Chemistry - University of Natural Resources and Applied Life Sciences
Muthgasse 18
A-1190 Wien
T +43/1/36006-6092
Thomas.prohaska(at)boku.ac.at

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Vienna, July 7, 2003