Remains of the day-preservation of organic micro-residues on stone tools

Here I report on the decay processes of microscopic organic residues left on stone tool surfaces after their use. Residue analysis on ancient stone tools facilitates reconstruction of past activities. This study enables predictions about the circumstances under which ancient residues preserve. Experimental tool sets with modern residues were buried for a year in separate deposits at Sterkfontein, Sibudu (South Africa) and Zelhem (the Netherlands) whose pH and geomorphology varied, they were then analysed using light microscopy. Biological weathering mainly causes residue decay. In unstable environments rich in microbes and micro-organisms, residues decay quickly. From an archaeological perspective this means that sites that are stable, desiccated, waterlogged, extremely acidic or alkaline and extremely cold or hot sites. Different residue types have different preservation optima and this may lead to a preservation and perhaps interpretation bias. The preliminary predictive models presented in this paper could aid in the considered selection of sites and samples.