The exceptional abandonment of metal tools by North American hunter-gatherers, 3000 B.P.

Abstract

Most prehistoric societies that experimented with copper as a tool raw material eventually abandoned stone as their primary medium for tool making. However, after thousands of years of experimentation with this metal, North American hunter-gatherers abandoned it and returned to the exclusive use of stone. Why? We experimentally confirmed that replica copper tools are inferior to stone ones when each is sourced in the same manner as their archaeological counterparts and subjected to identical tasks. Why, then, did copper consistently lead to more advanced metallurgy in most other areas of the world? We suggest that it was the unusual level of purity in the North American copper sourced by North American groups, and that naturally occurring alloys yielded sufficiently superior tools to encourage entry into the copper-bronze-iron continuum of tool manufacture in other parts of the world.

Raw material optimization and stone tool engineering in the Early Stone Age of Olduvai Gorge (Tanzania)

“…[35,[37][38][39]). Only recently has archaeological literature used similar techniques to answer Palaeolithic questions [32,33]. Here, we adapt the techniques used during fracture mechanics research [35,37], and improve on those used previously for archaeological purposes [32], to compare the sharpness and durability of the three raw materials used to produce stone tools at Olduvai Gorge.…”

“…muscular tissue), while also maintaining identical material conditions for each cutting test. Previous experiments using similar materials have proven its efficacy for sharpness tests [32,33,39]. Tubing was secured using a steel frame and pulled taut (but not stretched) perpendicular to the flake's cutting edge.…”

“…Only recently have archaeologists started to investigate the attribute of edge sharpness empirically [31][32][33][34]. Controlled cutting tests have previously been used to record mechanical definitions of this attribute on lithic objects [32,33], following techniques regularly applied within fracture mechanics research [35][36][37]. Here, we apply a similar experimental procedure that allows the force (N), work (J) and material deformation (mm) required for a stone edge to initiate cuts in a material to be recorded.…”

Heat treatment significantly increases the sharpness of silcrete stone tools

“…Our target cutting material was 2mm thick polyvinyl chloride (PVC) tubing. Previous experiments have demonstrated how this PVC tubing ) and other similar materials (McCarthy et al 2010;Torchy 2015;Schuldt et al 2016;Key et al 2018;Bebber et al 2019) allow comparable conditions between cutting tests while simultaneously providing a material that allows for deformation before stiffening and fracturing (in a manner similar to biological tissues; Atkins 2009). The PVC tubing was secured onto a steel frame such that it was fully extended (but not stretched) and perpendicular to both the direction of cutting motion and the length of the flake's cutting edge (Fig.…”

“…Archaeologists recently introduced mechanical tests of stone tool edge sharpness to Palaeolithic research. Their experiments investigate how sharpness varies between stone edges made from different raw materials , how stone cutting edges perform relative to copper alternatives (Bebber et al 2019) and the rate that a stone's edges blunt (Key et al 2018). These studies are part of a broader movement within archaeology to apply mechanical research techniques to answer functional questions (e.g., Key 2016;Milks et al 2016;Bebber 2017;Thomas et al 2017;Kozowyk and Poulis 2019;Schmidt et al 2019;Calandra et al 2020;Key and Lycett 2020;Marreiros et al 2020).…”