August 14, 2009

Early Man Used Heat To Make Stronger Tools

Thousands of years ago, early humans formed higher quality stone tools by putting the rocks in a fire.

The 72,000-year-old evidence has been dug up in Africa, researchers announced in of the journal Science.

The discovery predates the first evidence of this kind of skill by 45,000 years, reported Curtis Marean, a paleoanthropologist at the Institute of Human Origins, and a co-writer of the report.

"Heat treatment technology begins with a genius moment - someone discovers that heating stone makes it easier to flake," Marean said in a statement.

"This knowledge is then passed on, and in a way unique to humans, the technology is slowly ratcheted up in complexity as the control of the heating process, cooling and flaking grows in sophistication."

The researchers discovered items constructed from a silcrete rock, which is a brittle material. However, heating it alters the color and the grain structure, making it a lot sturdier.

"When I returned to dig the stone out the following day, the results were amazing. After heating, the silcrete became a deep red color and was easily flaked.
Most importantly, it looked exactly like silcrete from site PP5-6. Using heated silcrete we were then able to produce realistic copies of the actual silcrete tools," said lead author Kyle Brown.

To verify their theory, the researchers baked silcrete overnight. The next morning, they discovered that they could shape it into tools that look close to the ones they dug up at the archaeological site in South Africa, near the Indian Ocean.

The ingenious tools would have been perfect for hunting, the researchers noted.

"Here are the beginnings of fire and engineering," noted Brown.

John Webb and Marian Domanski of La Trobe University in Australia responded to the report by saying that the advance of heat treatment could have influenced early modern humans to move from Africa to colder areas like Europe.

"Our discovery shows that these early modern humans had this complex cognition," Brown says.

"This expression of cognitive complexity in technology by these early modern humans on the south coast of South Africa provides further evidence that this locality may have been the origin location for the lineage that leads to all modern humans, which appeared between 100,000 and 200,000 years ago in Africa," explains Marean.

"There is no consensus as to when modern human behavior appears, but by 70,000 years ago there is good evidence for symbolic behavior," he says. "Many researchers are looking for technological proxies for complex cognition, and heat treatment is likely one such proxy."

"Prior to our work, heat treatment was widely regarded as first occurring in Europe at about 25,000 years ago," Marean says. "We push this back at least 45,000 years, and, perhaps, 139,000 years, and place it on the southern tip of Africa at Pinnacle Point."


Image 2: Evidence reported in the Aug. 14 issue of the journal Science shows that early humans living on the southern coast of Africa 72,000 years ago used a complex heat treatment process to manufacture blades and bifacial tools. Unheated silcrete (left) can show dramatic changes in color and texture after heating and flaking (right). An international team, including three researchers from the Institute of Human Origins at Arizona State University, note that silcrete is not found closer than 5 kilometers from their excavation at Pinnacle Point, Mossel Bay, South Africa, and that most pieces found are extensively flaked. Credit: Photo by Kyle Brown/South African Coast Paleoclimate, Paleoenvironment, Paleoecology, Paleoanthropology Project (SACP4)


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