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Ancient humans used controlled fire to modify their stone tools at聽least 300,000 years ago.

Previously, the oldest hard evidence of controlled fire use was from Pinnacle Point in South Africa, 164,000 years ago. 鈥淲e just doubled it,鈥� says Filipe Natalio of the Weizmann Institute of Science in Israel. He and his colleagues studied 300,000-year-old flint tools from Qesem cave in Israel. The cave was occupied between 420,000 and 200,000 years ago, and the people who lived there regularly lit fires.

Careful heating can change the crystal structure of rocks and make them easier to shape into tools such as blades. However, until now it has rarely been possible to determine which stone tools have been heated. Some bear characteristic fractures, which indicate they were heated, but these don鈥檛 always form.

鈥淚t can also be misleading,鈥� says聽Mareike Stahlschmidt at the聽Max Planck Institute for Evolutionary Anthropology in Germany. That is because stones also fracture when they freeze.
Natalio鈥檚 team has developed a method that uses spectroscopy to examine the atomic structure of stone tools, revealing any alterations caused by heating.

鈥淲e can see fire where you don鈥檛 see it visually,鈥� says Natalio. The team found that many of the stone tools from Qesem cave had been heated. Primitive flakes were heated to over 400掳C, but the more advanced blades were heated more gently, to temperatures of around 250掳C.

These lower temperatures were less likely to shatter the blades when people worked them, but also required more control over the fire. Natalio says the blades probably weren鈥檛 placed directly in the fire, which would be too hot, but instead buried in sediment with a fire on top 鈥� a trick some people still use to slow-cook large pieces of meat.

鈥淪uch heat treatment would indicate complex behaviour,鈥� says Stahlschmidt. 鈥淧eople are intentionally changing the properties of a raw material to get what they need.鈥�

It is unclear who the inhabitants of Qesem cave were. The oldest evidence of Homo sapiens is from around 300,000 years ago in Morocco, and there is no evidence of modern humans outside Africa before 210,000 years ago. There is good evidence that Neanderthals had control of fire, and other hominins may also have done so. The cave has only yielded one hominin tooth, and it is so badly eroded that the species of its owner can鈥檛 be identified.

It also isn鈥檛 clear when ancient humans first began using fire, and when they learned to control it 鈥� as opposed to opportunistically making use of natural wildfires.

Ash and burnt bone have been found in Wonderwerk cave in South Africa and dated to 1 million years ago, and fires burned at Gesher Benot Ya鈥榓qov in Israel to nearly 790,000 years ago. But Stahlschmidt says neither site has unambiguous evidence for controlled use of fire.