Fire engineers of the Stone Age: Africans heated stones for toolmaking 72,000 years ago.

Stone Age toolmakers didn't need motivational speakers to get fired up at work. People living on the southern tip of Africa 72,000 years ago decided on their own to heat stones with controlled fires to make the rock more suitable for tool manufacturing, a new study finds.

Coastal residents of southern Africa may even have heated stones as a first step in toolmaking as early as 164,000 years ago, report Kyle Brown of the University of Cape Town, South Africa, and his colleagues in the Aug. 14 Science. Until now, evidence of heat treatment extended back no further than about 25,000 years ago in Europe, Brown notes.

Brown's results "push the antiquity of heat treatment back much earlier than previously supposed," says John Shea of Stony Brook University in New York.

At South Africa's Pinnacle Point cave, the researchers identified magnetic and molecular signatures of intense heating on 26 tools made of a type of stone called silcrete. The tools came from an excavation of sediment layers dating to between 72,000 and 47,000 years ago. The team estimates that the artifacts were heated at maximum temperatures of 300[degrees] to 400[degrees] Celsius.

High levels of surface gloss further indicated that a majority of 153 stone artifacts from the same and nearby layers had been heated, probably before being made into tools. And gloss levels on 24 Pinnacle Point stone tools with an estimated age of 164,000 years suggested that they too had been heated at high temperatures.

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