Fire a Tool for Engineering?

There is a long standing debate in Archaeology as to when the modern behavior we see in humans appeared (Brown et. al. 2009: 859). Though the date of its emergence has been pushed back as far as back as 80 k years ago with evidence of symbolic behavior increasing all the time, some still argue that it emerged even earlier (Brown et. al. 2009: 859). These scientists argue that there is evidence that pushes this date as far back as Middle Stone Age (Brown et. al. 2009: 859). This evidence includes complex behaviors like the use of bone tools, composite tools, blades, and controlled use of fire (Brown et. al. 2009: 859).
This is where the article “Fire as an Engineering Tool of Early Modern Humans” comes in, Brown et. al. believe they can show not only controlled use of fire, but the use of fire to heat treat stones in order “to improve their flaking properties” as early as 164 ka (2009: 859 and 861). In order to prove this hypothesis, they started by looking at the ethnographic record and found that in Australia silcrete was heat treated and that this heat treatment by the indigenous knappers increased their ability to work with it (Brown et. al. 2009: 859). They then copied the process the indigenous groups used to heat treat these tools in order to gain an example of what to look for in ancient tools collected from the sites of Still Bay and Pinnacle Point to evaluate whether or not these tools had been heat treated (Brown et. al. 2009: 859). They copied this process by slowly heating silcrete 350 C and then flaked these rocks (Brown et. al. 2009: 859). They then ran a rebounded hardness tests on the experimentally created silcrete tool, this test can tell scientists whether or not a rock will fracture in a predictable manner (Brown et. al. 2009: 859). They found that the tools they created through heat treatment could be made with a finer cutting edge and fractured with greater predictability than those rocks that had not been heat treated, which would have allowed for the production of bifaces that was more efficient than rocks not heat treated (Brown et. al. 2009: 859-860). Brown et. al. also discovered that the heat treated specimens they created looked a lot like those collected from the site of Still Bay (2009: 859).
Brown et. al.’s next step was to show that burnt tools from these archaeological sites were not being altered accidentally by hearths or bush fires (Brown et. al. 2009: 860). In order to do this they preformed three tests on slicrete tools from the two aforementioned archaeological sites (Brown et. al. 2009: 860). The first was a mineral magnetic analysis, which is meant to show whether or not these artifacts have a large amount of burnt sediment or are “combustion features” (Brown et. al. 2009: 860). Neither of these features was present in the artifacts, which according to this test means that these artifacts were not accidently burned (Brown et. al. 2009: 860). The second test they preformed was Palaeomagnetic analysis which can tell researchers if the natural direction of the magnetic field has been altered by being heated to a temperature above the Curie point (Brown et. al. 2009: 860). This magnetic field can also be partially altered if the temperature the rocks are heated to a temperature that is under a rock's Curie point (Brown et. al. 2009: 860). When Brown et. al. preformed this test they found that these tools were heated to temperatures between 300 to 400 degrees C, which is the normal temperature range that hearths can reach in South Africa not only today, but in prehistoric times as well (2009: 860). The final test was a maximum gloss test which simply shows whether or not the flaked surface is more reflectant than usually, greater reflectance indicates that a rock has been heat treated before it was flaked (Brown et. al. 2009: 860). This test showed that these archaeologically discovered tools had been heat treated before they were flaked due to their high level of gloss (Brown et. al. 2009: 860). Thus, all the tests performed showed that these tools were not accidently burnt, but were heat treated (Brown et. al. 2009: 860).
Brown et. al. has done a very good job of showing that not only was heat treating technology an effective way of increasing a rocks flaking ability, but also that these rocks heat treatment did not happen accidentally (2009: 859-860). They did not use just one test to do this either, they used multiple tests which allowed these scientists to back up their findings (Brown et. al. 2009: 859-869). They did such a good job that there only appears to be one problem with their analysis, small sample size (Brown et. al. 2009: 860). For example, when they performed their palaeomagnetic analysis they were only able to use 13 of the rocks from those they sampled (Brown et. al. 2009: 860). Otherwise, this analysis of a complex behavior from the Middle Stone Age is a very good addition to the increasing proof that modern human behavior arose very early in our evolution (Brown et. al. 2009: 859).

By: Laura Bailey






Work Cited
Brown, Kyle S., Curtis W. Marean, Andy I. R. Herries, Zenobia Jacobs, Chantel Tribolo, David Braun, David L. Roberts, Micheal C. Meyer, and Jocelyn Bernatchez
2009 Fire as a Engineering Tool of Early Modern Humans. Science 325: 859-862.