Lately there has been great renewed interest in the question of when hominins first controlled and produced fire. We are working on this topic from a number of perspectives. First, to better understand what temperatures are needed to leave an impact on proxies for fire such as stone tools, bones and sediments, we built a heating apparatus to do a set of controlled experiments heating various sediment types to different temperatures of varying durations. The results (see Aldeias et al., 2016a; Aldeias, in press) show that average fires produce subsurface temperatures high enough to cause thermal alteration of objects up to 10 cm below the surface (with maximum temperatures at this depth ranging from 85°C up to ~250°C). This apparatus is available for additional experiments.
Second, we have also started to investigate the effects of cooking, namely concerning the exploitation of marine resources. We have conducted a series of experiments on shellfish roasting fires (Aldeias et al., 2016b). In this work, we use FTIR to trace the transformation of aragonitic shells to calcite and we show that this transformation can start at fairly low temperatures (around 250 °C). This research highlights potential issues of using altered shells for radiocarbon and isotope analysis. Additional papers, focusing on using microFTIR to map the location of the aragonite>calcite transformation within a shell and application of this new methodology in archaeological sediments, are in preparation.
Third, in our excavations we continue to document the relative presence of fire related activities through, where possible, the documentation of fire features (including the application of micromorphology and microFTIR) and also through the quantification of fire proxies such as heated stone and heated bones. We are quite interested in expanding this data set to have a better understanding of when hominins were making use of fire in part to better understand the origins of the controlled use and production of fire.