Ancient toolmakers’ fiery secret

[Image] Heat-treated silcrete (right) and
untreated silcrete (left).
(Image: Kyle Brown, SACP4)

MEDIA CONTACTS
Lynne Cable
Department of Archaeology, UCT
+27 21 650 2353
Curtis Marean
Institute of Human Origins, ASU
+1 480 727 6580

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• Science
• University of Cape Town
• Institute of Human Origins, Arizona
State University

Janine Erasmus

New evidence has emerged that 72 000 years ago ancient Southern Africans used pyrotechnology, or the controlled use of fire, to make stone tools.

This pushes back the earliest signs of heat treatment by at least 45 000 years and signals a breakthrough in human evolution, researchers say.

The results of research carried out by an international team of scientists from the universities of Arizona, Liverpool, New South Wales, Bordeaux, Wollongong, and Cape Town were published in the journal Science in mid-August 2009.

Studies were carried out at Pinnacle Point, a sea cave in the cliffs near Mossel Bay on South Africa’s southern Cape coast. Signs of occupation show that the first inhabitants arrived at the site 164 000 years ago.

Kyle Brown, an archaeology doctorate student at Cape Town University whose research focuses on experimentally replicating ancient tools, was the study leader and the paper’s chief author.

Brown is also a director at the South African Coast Paleoclimate, Paleoenvironment, Paleoecology, Paleoanthropology Project (SACP4), located at Pinnacle Point.

Tool making

Over the course of his research, Brown noticed that many ancient arrowheads and other implements found at the site were made of silcrete, a conglomerate of gravel and sand cemented by silica.

Ancient inhabitants of the time used the technique of flaking, or hitting one piece of rock with another to chip off sharp flakes, to make spearheads or meat-cutting implements. The smaller of the two pieces so produced is the flake, while the larger one is the core. The core may be used again to produce more flakes until it is completely reduced.

Wishing to reproduce the tools, the researchers tried to locate the silcrete’s source but, said Brown, they could not find any that matched the fine-grained, reddish implements they found at the site.

The idea of heat treatment was sparked by their fortunate discovery of a large piece of silcrete, almost 10cm in diameter, embedded in ash.

This chunk, said Brown, looked “like it had been accidentally lost in a fire pit”. Then the idea of heat treatment occurred, and the team began to test the silcrete in fires, burying stones in the sand and building a fire on top, keeping it going for hours at a time.

After some experimentation, according to the Science report, they were able to make exact replicas of the glossy, reddish implements found in the Pinnacle Point cave.

But heat-treated tools were no accident. It took the team a long time to find the right recipe, which called for between 20kg and 40kg of hardwood, and a firing time of around 30 hours with the stone item buried under the coals. It took a lot of planning for ancient people to successfully complete this process, said Brown.

Further tests were needed to substantiate the theory. These included archaeomagnetic analysis, which works on the fact that heating changes the stone’s magnetic polarity; optically stimulated luminescence dating, which measures the time since material containing crystalline structures was heated or exposed to sunlight; and maximum gloss, which measures reflectance of the surface.

Evolutionary breakthrough

The research team views the development of controlled heat treatment as a breakthrough in human evolution.

Heat treatment is a behaviour traditionally associated with the Upper Palaeolithic epoch (45 000 – 10 000 years ago), but Pinnacle Point features only a large Middle Palaeolithic (300 000 – 30 000 years ago) occupation. The Palaeolithic era is distinguished by the development of the first stone tools.

Skilfully using heat to modify stone required a cognitive link between improved flaking qualities and other changes in the material, and fire. This could indicate that complex thinking may have developed earlier than previously thought.

“These early modern humans commanded fire in a nuanced and sophisticated manner,” said Brown. “This is the beginnings of fire and engineering, the origins of pyrotechnology, and the bridge to more recent ceramic and metal technology.”

Even more exciting are indications that heat treatment could have begun at Pinnacle Point at the same time that people moved in – that is, 164 000 years ago.

According to the study, the earliest signs of heat treatment of stone were previously seen in Europe, and no later than 25 000 years ago.

“We push this back at least 45 000 years,” said project director and co-author Curtis Marean, a paleoanthropologist with Arizona University’s Institute of Human Origins in the US, “and perhaps 139 000 years, and place it on the southern tip of Africa at Pinnacle Point.”

Other significant behaviours discovered at Pinnacle Point include the harvesting of shellfish for food, and the use of ochre pigment for personal adornment.

The paper concludes that such an early expression of cognitive ability in technology gives further impetus to the theory that the southern tip of Africa is the origin of modern humans’ genetic lineage.

Modern humans appeared between 100 000 and 200 000 years ago in Africa, leaving the continent about 50 000 years ago for the cooler climates of Europe and Asia. The Neanderthals living there at the time died out eventually, leaving modern humans to populate the northern and southern continents.

Marean said their discovery provides a reasonable explanation for the rapid spread of modern humans over their new domain. “They were masters of fire and heat and stone, a crucial advantage as these tropical people penetrated the cold lands of the Neanderthal.”

Marean goes on to describe the Pinnacle Point team as a leader in revealing the process of how humans developed into the species they are today.