Modern humans may have been using fire to make tools more than 30,000 years earlier than once thought, according to archaeologists working in a string of rocky caves along the South African coast. At Pinnacle Point, researchers have found evidence that people began heat-treating stone to make it easier to shape into tools about 70,000 years ago and possibly as early as 164,000 years ago. The find adds to the evidence that a wide range of sophisticated behaviors--from advanced toolmaking to symbolism--were flourishing around the same time.
The discovery has its roots in experimental archaeology. Kyle Brown, an archaeologist at the University of Cape Town in South Africa, and colleagues were trying to recreate the axes and hafted tools they were finding in the Pinnacle Point caves--a site containing many artifacts of early human activity--to learn more about how they were made. One of the local rocks that these early humans fashioned tools from is silcrete, which is similar to flint. But when the researchers tried to recreate the tools, they couldn't quite get it right. "We were having a really hard time coming up with [something] that looked like what we were finding at the site," Brown says.
So the researchers began experimenting with heat treatment. After much trial and error, they found that it took 20 to 40 kilograms of hardwood and almost 30 hours to create the 300°C temperatures in silcrete needed to fashion tools like those seen at Pinnacle Point. Those conditions alone were a good sign that the stone tools were no campfire accident, the team reports tomorrow in Science. "It requires a lot of planning," Brown says. "It's not the kind of thing people would do with an ordinary cooking fire." Heating makes the stones easier to flake and shape into blades.
The team also applied several different tests to confirm that the heat-treated stones had been used as tools. Stones flaked after heating have distinctive characteristics that can be measured and detected using thermoluminescence, magnetic analysis, and maximum gloss, a measurement of reflectance.
Previous analysis indicates that the clearly heat-treated tools are more than 70,000 years old, meaning that humans were using fire to improve tools at this time. The dating coincides with a wave of discoveries from Pinnacle Point and other sites in South Africa that suggest that a wide range of sophisticated behaviors--from toolmaking to personal decoration and symbolism--were all flourishing at about the same time. "We have an explosion of complex behaviors at sites in South Africa at this period," says Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
The find also adds weight to the argument that modern humans were acting in sophisticated ways long before they came to Europe about 35,000 years ago--and that they were engaged in far more complex behavior than were the Neandertals who lived at the same time, says anthropologist Alison Brooks of George Washington University in Washington, D.C. "This is another piece of evidence that modern humans had made a lot of discoveries that Neandertals had not."
Brown argues that the technique he and his team developed may help archaeologists determine when humans first used heat treatment. "This is a bridging technology between control of fire and the later production of ceramics and metalworking," he says. "There's a long gap, but I think as people begin to look for heat-treatment they'll begin to see it."