title: A previously undescribed organic residue sheds light on heat treatment in the Middle Stone Age.
abstract: South Africa has in recent years gained increasing importance for our understanding of the evolution of 'modern human behaviour' during the Middle Stone Age (MSA). A key element in the suite of behaviours linked with modern humans is heat treatment of materials such as ochre for ritual purposes and stone prior to tool production. Until now, there has been no direct archaeological evidence for the exact procedure used in the heat treatment of silcrete. Through the analysis of heat-treated artefacts from the Howiesons Poort of Diepkloof Rock Shelter, we identified a hitherto unknown type of organic residue - a tempering-residue - that sheds light on the processes used for heat treatment in the MSA. This black film on the silcrete surface is an organic tar that contains microscopic fragments of charcoal and formed as a residue during the direct contact of the artefacts with hot embers of green wood. Our results suggest that heat treatment of silcrete was conducted directly using an open fire, similar to those likely used for cooking. These findings add to the discussion about the complexity of MSA behaviour and appear to contradict previous studies that had suggested that heat treatment of silcrete was a complex (i.e., requiring a large number of steps for its realization) and resource-consuming procedure.
authors.affiliation: Eberhard Karls University of Tübingen, Department of Prehistory and Quaternary Ecology, Schloss Hohentübingen, 72070 Tübingen, Germany. Electronic address: patrick.schmidt@uni-tuebingen.de.
authors.forename: Patrick
authors.initials: P
authors.lastname: Schmidt
authors.affiliation: CNRS, USR 3336, UMIFRE 25, Institut Français d'Afrique du Sud (IFAS), Johannesburg, South Africa; Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Porraz
authors.affiliation: Sorbonne Universités, UPMC Université Paris 6, MONARIS "de la Molécule aux Nano-objets: Réactivité, Interactions et Spectroscopies", UMR 8233, UPMC-CNRS, 4 place Jussieu, 75252 Paris Cedex 5, France.
authors.forename: Ludovic
authors.initials: L
authors.lastname: Bellot-Gurlet
authors.affiliation: University of Cape Town, Department of Biological Sciences, Rondebosch 7701, South Africa.
authors.forename: Edmund
authors.initials: E
authors.lastname: February
authors.affiliation: Eberhard Karls University of Tübingen, Institute for Archaeological Sciences, Rümelinstrasse 23, 72070 Tübingen, Germany.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Ligouis
authors.affiliation: Sorbonne Universités, UPMC Université Paris 6, MONARIS "de la Molécule aux Nano-objets: Réactivité, Interactions et Spectroscopies", UMR 8233, UPMC-CNRS, 4 place Jussieu, 75252 Paris Cedex 5, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Paris
authors.affiliation: CNRS, UMR 5199-PACEA, Université de Bordeaux 1, Talence, France.
authors.forename: Pierre-Jean
authors.initials: PJ
authors.lastname: Texier
authors.affiliation: University of Cape Town, Department of Archaeology, Rondebosch 7701, South Africa.
authors.forename: John E
authors.initials: JE
authors.lastname: Parkington
authors.affiliation: Eberhard Karls University of Tübingen, Institute for Archaeological Sciences, Rümelinstrasse 23, 72070 Tübingen, Germany.
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Miller
authors.affiliation: EberhardKarls University of Tübingen, Department of Geosciences, Applied Mineralogy, Wilhelmstraße 56, 72074 Tübingen, Germany.
authors.forename: Klaus G
authors.initials: KG
authors.lastname: Nickel
authors.affiliation: Eberhard Karls University of Tübingen, Department of Prehistory and Quaternary Ecology, Schloss Hohentübingen, 72070 Tübingen, Germany.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Conard
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005390:Fires; D049690:History, Ancient; D015186:Hominidae; D006358:Hot Temperature; D006801:Humans; D012822:Silicon Dioxide; D013638:Tars / Q000737:chemistry; D013672:Technology / Q000266:history / Q000379:methods*; D053001:Tool Use Behavior
chemical_list: D013638:Tars; D012822:Silicon Dioxide
keywords: Modern behaviour; Residue analysis; Silcrete heat treatment; Transformative technology