Klipdrift Shelter (Af. Du Sud): Middle Stone Age Humans Used Innovative Heating Techniques to Make Tools
Early humans living in southern Africa in the Middle Stone Age after 65,000 years ago used advanced heating techniques to produce silcrete blades, according to a new study.
This image shows heated silcrete artifacts made by Middle Stone Age humans at Klipdrift Shelter, South Africa. Image credit: Katja Douze / University of the Witwatersrand.
South African Middle Stone Age humans deliberately heated silcrete, a hard, fine-grained, local rock, so that they could more easily obtain blades from the core material. The blades were then crescent shaped and glued into arrow heads.
“This is the first time anywhere that bows and arrows were used. This would have had a major effect on hunting practices as both spears and bow and arrow could be used to hunt animals,” said study senior author Prof. Christopher Henshilwood, from the University of the Witwatersrand in Johannesburg, South Africa, and the University of Bergen in Norway.
The extensive heat treatment enabled early humans to produce tougher, harder tools — the first evidence of a transformative technology. However, the exact role of this important development in the Middle Stone Age technological repertoire was not previously clear.
Prof. Henshilwood and his colleagues addressed this issue by using a new non-destructive approach to analyze the heating technique used in the production of silcrete artifacts at Klipdrift Shelter, a recently discovered Middle Stone Age site located on the southern Cape of South Africa, including unheated and heat-treated comparable silcrete samples from 31 locations around the site.
The researchers noted intentional and extensive heat treatment of over 90% of the silcrete, highlighting the important role this played in silcrete blade production.
The heating step appeared to occur early during the blade production process, at an early reduction stage where stone was flaked away to shape the silcrete core.
The hardening, toughening effect of the heating step would therefore have impacted all subsequent stages of silcrete tool production and use.
“Heating was applied, non-randomly, at an early stage of core exploitation and was sometimes preceded by an initial knapping stage,” said co-author Dr. Karen van Niekerk, from the University of Bergen.
“As a consequence, the whole operational chain, from core preparation to blade production and tool manufacturing, benefited from the advantages of the heating process.”
The scientists suggest that silcrete heat treatment at the Klipdrift Shelter may provide the first direct evidence of the intentional and extensive use of fire applied to a whole lithic chain of production.
Along with other fire-based activities, intentional heat treatment was a major asset for Middle Stone Age humans in southern Africa, and has no known contemporaneous equivalent elsewhere.
“The advantages of the heating process are multiple: by reducing the material’s fracture toughness and increasing its hardness, less force was needed to detach blades after heat treatment, resulting in better control and precision during percussion,” Prof. Henshilwood explained.
“This heating process marks the emergence of fire engineering as a response to a variety of needs that largely transcend hominin basic subsistence requirements, although it did not require highly specialized technical skills and was likely performed as part of on-site domestic activities,” he said.
The research was published this week in the journal PLoS ONE.
Delagnes A. et al. 2016. Early Evidence for the Extensive Heat Treatment of Silcrete in the Howiesons Poort at Klipdrift Shelter (Layer PBD, 65 ka), South Africa. PLoS ONE 11 (10): e0163874; doi: 10.1371/journal.pone.0163874