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Early modern humans didn’t just chip away at stones to create their tools. They treated stone with fire in a sophisticated fashion, according to research published August 14th in the journal Science.

About 72,000 years ago, our ancestors along coastal¹ South Africa made tools from silcrete, a cement-like layer of soil. The silcrete found at archaeological sites was glossy² with a fine grain and a reddish color. It didn’t match stones in local outcroppings. Researchers from the University of Cape³ Town couldn’t find big enough pieces to learn more, until a couple of years ago. Then a colleague from Arizona State University remarked that a piece of silcrete reminded him of heat-treated tools in the Southwest.

So the researchers set up a fire pit and buried a silcrete sample at high temperature. The next day, the stone looked like ones used by early humans. It flaked⁴ easily and provided the basic material for complex tools. Until now, heat treatment was thought to have started in Europe 25,000 years ago. This discovery pushes it back tens of thousands of years into Africa—and suggests that the southern African coast may have been the site of a truly Promethean revolution.