Israel scientists from the Weizmann Institute of Science, using an advanced, innovative method they developed to detect nonvisual traces of fire, have detected the usage of fire at least 800,000 years ago, one of the earliest known pieces of evidence for the use of fire.
The newly developed technique may provide a push toward a more scientific, data-driven type of archaeology, and could help to “better understand the origins of the human story, our most basic traditions and our experimental and innovative nature.”
Scientists say the controlled use of fire by ancient hominins, a group that includes humans and extinct human species, is hypothesized to date back at least a million years, to around the time that archaeologists believe Homo habilis began its transition to Homo erectus. The working theory, called the “cooking hypothesis,” is that the use of fire was instrumental in our evolution, not only for allowing hominins to stay warm, craft advanced tools and ward off predators but also for acquiring the ability to cook. Cooking meat not only eliminates pathogens but increases efficient protein digestion and nutritional value, paving the way for the growth of the brain.
The only problem with this hypothesis is a lack of data: since finding archaeological evidence of pyro technology primarily relies on visual identification of modifications resulting from the combustion of objects, mainly a color change.
Traditional methods have managed to find widespread evidence of fire use no older than 200,000 years. While there is some evidence of fire dating back to 500,000 years ago, it remains sparse, with only five archaeological sites around the world providing reliable evidence of ancient fire.
“We may have just found the sixth site,” says Dr. Filipe Natalio of Weizmann’s Plant and Environmental Sciences Department, whose previous collaboration with Dr. Ido Azuri, of Weizmann’s Life Core Facilities Department, and colleagues provided the basis for this project. Together they pioneered the application of Artificial Intelligence (AI) and spectroscopy in archaeology to find indications of the controlled burning of stone tools dating back to between 200,000 and 420,000 years ago in Israel.
Researching at the Evron Quarry, located in the Western Galilee, is an open-air archaeological site that was first discovered in the mid-1970s, archaeologists dug down 14 meters and uncovered a large array of animal fossils and Paleolithic tools dating back to between 800,000 and 1 million years ago, making it one of the oldest sites in Israel. None of the finds from the site or the soil in which they were found had any visual evidence of heat, as ash and charcoal degrade over time, eliminating the chances of finding visual evidence of burning. Thus, if the Weizmann scientists wanted to find evidence of fire, they had to search farther afield.
“We tested a variety of methods, among them traditional data analysis methods, machine learning modeling and more advanced deep learning models,” says Azuri, who headed the development of the models. “The deep learning models that prevailed had a specific architecture that outperformed the others and successfully gave us the confidence we needed to further use this tool in an archaeological context having no visual signs of fire use.”
The advantage of AI is that it can find hidden patterns across a multitude of scales. By pinpointing the chemical composition of materials down to the molecular level, the output of the model can estimate the temperature to which the stone tools were heated, ultimately providing information about past human behaviors.
With an accurate AI method, the team searched for molecular signals from the stone tools used by the inhabitants of the Evron Quarry almost a million years ago. To this end, the team assessed the heat exposure of 26 flint tools found at the site almost half a century ago.
The results revealed that the tools had been heated to a wide range of temperatures – some exceeding 600°C. In addition, using a different spectroscopic technique, they analyzed 87 faunal remains and discovered that the tusk of an extinct elephant also exhibited structural changes resulting from heating. While cautious in their claim, the presence of hidden heat suggests that our ancient ancestors were experimentalists.
According to the research team, by looking at archaeology from a different perspective, and using new tools, we may find much more than we initially thought. The methods they’ve developed could be applied, for example, at other Lower Paleolithic sites to identify nonvisual evidence of fire use. Furthermore, this method could perhaps offer a renewed spatiotemporal perspective on the origins and controlled use of fire, helping us to better understand how hominin’s pyro technology-related behaviors evolved and drove other behaviors.