It’s not always easy to find clues to old campfires. Pieces of charcoal, cracked bones and discolored rocks often give off a prehistoric glow. But not every fire leaves such clear marks, especially after hundreds of thousands of years.
Now, using artificial intelligence (AI) to detect the subtle ways in which extreme heat distorts a material’s atomic structure, scientists have discovered the potential presence of a nearly 1 million-year-old fire with dozens of supposedly burnt objects buried at an archaeological site. site. place in Israel. If the technique proves reliable, the findings could shed light on when, where and why people first learned to harness the flame.
Richard Wrangham, an anthropologist at Harvard University, is impressed with the new method. He has long argued that our human ancestors developed smaller guts and bigger brains as soon as they started cooking food, perhaps about 1.8 million years ago. “We need imaginative new methods” to locate old fires, he says. “Now we have one.”
Most studies of fire are based on the obvious bits of charcoal and other clues. But Filipe Natalio, an archaeological biochemist at the Weizmann Institute of Science, wanted to find a way to identify the invisible evidence that fire leaves behind. Previous work, led in part by forensic scientists, has shown that combustion changes bone structure at the atomic level so that burned and unburned human bones absorb different wavelengths of the infrared spectrum. Researchers can detect a charred bone using a technique known as Fourier-transform infrared (FTIR) spectroscopy, which measures the absorption of different wavelengths of light.
Natalio and colleagues wondered if a similar method might work for burnt stone tools, which are often more abundant than bones in very ancient sites — and are a clear sign of human presence. He and his colleagues experimented by heating flint, a common rock for making tools that are easier to machine and shape when heated, to different temperatures in a fire, and then applying spectroscopic techniques to see if they had the characteristics of combustion. But due to natural variations in the flint, the patterns in the data were hopelessly complex.
“One peak would go up, the other would go down…and the changes were so subtle that we couldn’t rely on them,” says Natalio. “Then we switched to artificial intelligence.”
The researchers devised a computer program to hunt for subtle patterns that would have taken scientists ages to find on their own, Natalio says. The AI worked. Using a technique called ultraviolet (UV) Raman spectroscopy, which measures the absorption of UV light, the AI was able to reliably distinguish between burned and unburned pieces of modern flint and even reveal the temperatures at which they burned.
The team then applied their method to 26 flint tools, mostly small cutting edges, unearthed in the 1970s at Evron Quarry, a coastal town in northwestern Israel. A combination of dating methods suggested the site was between 800,000 and 1 million years old and was likely inhabited by the widespread tool-making human ancestor known as homo erectus† Dozens of animal bones were found in addition to the tools, but archaeologists had found no traditional evidence of fire, such as charcoal or red sediment.
Using their new technique, Natalio and colleagues found most of the flint tools were heated to a temperature range between 200°C and 600°Creport them today in the Proceedings of the National Academy of Sciences† (The average campfire burns at about 400°C.) The researchers also used FTIR spectroscopy to analyze 13 pieces of tusk, from one of two elephant-like genera known as Stegodon and Elephas, which was found in the same sedimentary layer as the tools. The tusks were also exposed to temperatures of up to 600°C.
That, Natalio says, could be evidence that the site’s inhabitants cooked their prey. If so, that would make it – along with a potential 1 million year old fireplace in South Africa’s Wonderwerk Cave, one of the oldest known cooking sites.
“It’s well done,” said Dennis Sandgathe, a paleoanthropologist at Simon Fraser University (the paper, not the roasted elephant). “There are less than half a dozen sites in the world with [evidence for] fire older than 500,000 years. It could be because humanoids didn’t use fire very often, but it could also be that we’re missing some of it. So this is very important.”
There’s still no way to say definitively whether the tools and tusks in this spot were burned in a natural or man-made fire, Natalio says. Based on vegetation, fires can burn at different temperatures even within one location. But the huge variability of temperatures between tools so close to Evron Quarry suggests to Natalio a radical idea: that the toolmakers were experimenting, heating flint cores to different temperatures to see how it affected their workability.
Sarah Hlubik, a paleoanthropologist at George Washington University who studies the origin of fire, isn’t so sure. “At the age of this site, I’d say that’s unlikely but not impossible,” she says. “We don’t see heat treatment until much later, and if the technology were experimented with after nearly 1 million years, we’d probably see it widespread sooner than we do.”
The new technique is promising, says Hlubik. But she’d like to see the work reproduced in a wider variety of settings — and for the team to rule out other possibilities, such as naturally burned material from different places and times pouring into the site. Until then, Hlubik says, “It’s important to take these kinds of results with a grain of salt.”