Laser ablation depth profiling of U-series and Sr isotopes in human fossils

We have explored laser depth profiling to obtain data sets for U-series as well as Sr analyses. Laser probing with an 81 gm spot size allows for the exploration of low uranium domains of up to 400 gm below the outer surface in tooth enamel. These low U domains will contain Sr isotope compositions of the individual, that are least affected by diagenetic Sr overprints. The small holes drilled for U surveying are not visible to the naked eye. Using larger spot sizes of around 233 gm, laser drilling can be used to obtain reliable U-series isotope data to a depth of approximately 1000 gm in enamel and around 1300 gm in bone. Furthermore, meaningful Sr-87/Sr-86 isotope data can also be obtained with this spot size. Using our sampling strategy, the overall damage to a human tooth is minute, as demonstrated on a Neanderthal tooth from Moula-Guercy. We expect that laser ablation depth profiling will become routine for gaining insights into the age of human fossils and the migrations of ancient humans. (C) 2013 Elsevier Ltd. All rights reserved.