Toolmaking technique 55,000 years older than we thought

Pressure flaking is a retouching technique that was used by prehistoric toolmakers to shape stone tips. They pressed the narrow end of a tool close to the edge of a piece they were working on to create rectangular, parallel marks; these are considered the hallmark of pressure flaking. This technique allowed them to more finely control the final shape and thinness of the tool edge than direct percussion could, and yielded sharp, thin, V-shaped tips with straight edges. The earliest evidence for pressure flaking came from the Upper Paleolithic Solutrean industry of Western Europe, and dates from around 20,000 years ago.

Most materials, except for obsidian, jasper, and some high-quality flint, need to be heat-treated before they can be pressure flaked. But as it turns out, those rectangular parallel marks that were thought to be diagnostic of pressure flaking only occur on flint, not on every material. This explains why pressure retouch was initially ruled out as a potential method used on some stone points recovered from the Blombos Cave, in South Africa. These tools date from the Middle Stone Age—about 75,000 years ago, and well before the European samples.

Using microscopic study and experimental replication, an international team has determined that pressure flaking was, in fact, used to make the Still Bay points. These are made of a stone called silicrete that needs to be heat treated before pressure flaking. The researchers confirmed heat treating by removing a flake and examining the scar under low magnification. If a flake is removed from unheated silicrete, the scar surface has a dull, rough texture; if the silicrete had been heated first, the scar is smooth and glossy.

Next, they collected silicrete from outcrops around 30km from Blombos cave, heated some of it, made points out of it, and used either pressure flaking or soft percussion to retouch them. They found that pressure flaking heated silicrete generated scars that were not always parallel or rectangular but are about twice as wide as those made when pressure flaking flint—just like those on the Blombos points. By comparing other attributes of the Blombos Still Bay points with the ones they made, the team concluded that at least half of the Blombos points were finished with pressure flaking.

Pretty obviously, this means that an apparently "modern" European toolmaking technique may have originated elsewhere and much, much earlier. And it seems to have arisen at a site where several other distinct technologies developed. The authors suggest that the use of pressure flaking at Still Bay "helps define it as a time when novel ideas and techniques were rapidly introduced."

Science, 2010. DOI: 10.1126/science.1195550  (About DOIs).