Identifying 1 Mya Fire in Wonderwerk Cave with Micromorphology and Fourier-Transform Infrared Microspectroscopy

The role of fire in the evolution of humans is an important yet unanswered question in palaeoanthropology, but there is a striking lack of archaeological evidence for the presence or absence of anthropogenic fire-use by early hominins. This is partially due to the difficulty of identifying fire residues, such as wood ash. I demonstrated that Fourier Transform Infrared Microspectroscopy integrated with micromorphological analysis can distinguish microscopic amounts of pyrogenic calcite which include wood ash, from non-pyrogenic calcites. The ν3 (CO3) peak, an absorption of energy by one of the three C-O bonds, is quantifiably more narrow in pyrogenic calcites. With the protocol, I evaluated potential evidence of anthropogenic fire at 1 Mya in Wonderwerk Cave, a South African archaeological site. The results confirmed the earlier identification of ashed plant remains in Stratum 10, thus supporting the association of fire and anthropogenic activity in Wonderwerk Cave in the Earlier Stone Age.