Ancient toolmakers discovered fire treatment for stone

Friday, August 14, 2009

WASHINGTON -- Maybe it was an accident or perhaps an ancient experiment.

Many thousands of years ago, early humans somehow figured out they could make better stone tools by treating the rocks with fire. Evidence of that, dating 72,000 years ago, has been found on the southeastern tip of Africa, researchers report in today's edition of the journal Science.

The find pushes back the first evidence of such technology by at least 45,000 years, according to Curtis Marean, a paleoanthropologist at the Institute of Human Origins at Arizona State University, a co-author 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. The new discovery is then passed on and improved.

The researchers found items made from a stone called silcrete, which usually was poor for tool making. But heating it causes it to change color and alter its grain structure, making it more usable.

To test their idea, the researchers heated some silcrete overnight. In the morning, they found they could flake it into shiny tools similar to the ones they found at the archaeological site in Pinnacle Point in South Africa, overlooking the Indian Ocean near Mossel Bay.

The silcrete tools would have been excellent as hunting weapons, knives and for exchange, the researchers said.

"Here are the beginnings of fire and engineering," said lead author Kyle Brown, a doctoral candidate at the University of Cape Town in South Africa.

John Webb and Marian Domanski of La Trobe University in Australia said in a commentary on the report that the development of heat treatment may have played a role in allowing early modern humans to spread from the milder African environment to colder, more hostile regions such as Europe.

It may have given them an advantage over the Neanderthals, who lacked this skill, noted Domanski and Webb, who were not part of the research team.

The research was funded by the U.S. National Science Foundation, the Hyde Family Trust and Arizona State University.

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