Strontium Isotope Analysis

The strontium isotope composition of tooth enamel can provide information about where an individual spent their child hood.
Strontium isotopes provide a fingerprint for different rock types and, as the distribution of rocks is well mapped in Britain and around the world, the geology provides the key to geographic location.
87Sr is formed by radioactive decay of 87Rb and it accumulates slowly through geological time. The 87Sr is normally expressed as a ratio against the stable 86Sr isotope as the 87Sr/86Sr ratio. In rocks that are old (>100 million years) and particularly if they also contain high levels of rubidium, the 87Sr/86Sr isotope ratio is high. This is typical of old granite and gneiss terrains. In rocks that are geologically young (<100 million year) and have low rubidium content the 87Sr/86Sr ratio is low. Rocks of this type tend to be recently erupted basalts. These values are transmitted, through the weathering of rocks to form soil, into the biosphere via plants and in drinking water. The range of 87Sr/86Sr ratios may seem very small, a typically low value would be 0.704 whereas 0.720 would be considered high, but such differences are easily measured to high levels of precision. The Bowmen’s teeth have a very high 87Sr/86Sr ratio.
Ideally, as with the Boscombe Bowmen, strontium isotope analysis is used in conjunction with other lines of evidence such as oxygen isotope analysis to constrain possible areas where an individual could have spent their childhood and/or rule out areas where the tooth data does not match environmental values.
Dr Jane Evans - British Geological Survey