Potential and pitfalls in establishing the provenance of earth-related samples in forensic investigations

Earth scientists are often asked to establish or constrain the likely provenance of very small quantities of earth-related material as part of a forensic investigation. We tested the independent and collective interpretations of four experts with differing analytical skills in the prediction of sample provenance for three samples from different environmental settings. The methods used were X-ray diffraction, scanning electron microscopy, the assessment of pollen assemblages, and structural characterization of organic matter at the molecular level. Independent interpretations were less accurate than those where multiple techniques were combined. Collective interpretation was very effective in the assessment of provenance for two of the three sites where the mineralogy and plant communities were distinctive. At the other site, although the mineralogical analysis correctly identified the Triassic mudstone soil parent material, Carboniferous spores from domestic coal were initially interpreted as deriving directly from bedrock. Such an interpretation could be a common pitfall owing to anthropogenic redistribution of material such as coal.