Finding clues to ancient campfires can be difficult. A prehistoric fire can be caused by bits of charcoal, cracked bones, and discolored rocks. After hundreds of thousands of years, blazes don't leave obvious traces.
Artificial intelligence has been used to detect the subtle ways in which extreme heat warps a material's atomic structure. The findings could shed light on when, where, and why humans first learned to use the flame.
The new method is being praised by Richard Wrangham. He believes that our human ancestors had larger brains and smaller guts when they first started cooking. He says there needs to be new methods to find ancient fires. We've got one now.
The obvious bits of charcoal are used in most studies of fire. Natalio wanted to find a way to identify the evidence left behind by fire. Burning alters bone structure at the atomic level, so burnt and unburnt human bones absorb different wavelength of the IR spectrum. The absorption of different wavelength of light can be measured using the FTIR technique.
Natalio and colleagues wondered if a similar method could work for burnt stone tools, which are often more abundant than bones in very ancient sites. After heating flint, a common toolmaking rock that can become easier to chip and shape after heating, he and colleagues applied spectroscopic techniques to see if they could identify the signatures of burning Natural variations in the flint made the data hopelessly complex.
The changes were so subtle that we couldn't rely on them. We turned to artificial intelligence when that happened.
The researchers created a computer program to look for subtle patterns that would take a long time to find on their own. The artificial intelligence was able to work. The artificial intelligence was able to distinguish burnt and unburnt pieces of modern flint using a technique called ultraviolet (UV) Raman spectroscopy.
The flint tools had been excavated in the 1970s from a coastal site in northwestern Israel. The site was thought to be between 800,000 and 1 million years old and inhabited by the widespread, toolmaking human ancestor known as Homo erectus. Dozens of animal bones were found next to the tools, but there was no evidence of fire.
Natalio and colleagues used a new technique to find that most of the flint tools had been heated to a range of temperatures between 200C and 600C. The average campfire is about 400C. 13 bits of tusk from one of two elephantlike generaes known as Stegodon and Elephas that had been found in the same layer as the tools were analyzed using FTIR. The temperatures were as high as 600C.
Natalio believes that the site's inhabitants cooked their kills. It would be among the oldest known cooking sites if that is the case.
Dennis Sandgathe is a paleoanthropologist at Simon Fraser University. Less than half a dozen sites in the world have evidence for fire that is more than 500,000 years old. It is possible that we are missing some of the fire that hominins used to use. This is crucial.
There is no way to say if the tools and tusks burned in a natural or human made fire. It is possible for a fire to burn at different temperatures in a single location. Natalio thinks that the toolmakers were experimenting with heating flint to different temperatures to see how it affects their workability.
Sarah Hlubik is a paleoanthropologist at George Washington University. She says that it is not impossible at the age of this site. If the technology was being used for nearly 1 million years, we would see heat treatment more widely than we do.
Hlubik is positive about the new technique. She would like to see the work reproduced in a variety of settings, and for the team to rule out other possibilities, such as naturally burnt materials from different places and times. Hlubik says it is important to take the results with a grain of salt.
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