Discovering ancient traces of fire

In an article published in Proceedings of the National Academy of Sciences (PNAS) in June 2022, Dr. Filipe Natalio of the Department of Plant and Environmental Sciences and Dr. Ido Azuri of the Department of Life Sciences Core Facilities described their novel method to detect nonvisual traces of fire dating back at least 800,000 years – 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 – perhaps more importantly – it could help us better understand the origins of the human story, our most basic traditions and our experimental and innovative nature.

The controlled use of fire by ancient hominins, a group that includes humans and some of our extinct family members, is hypothesized to date back at least a million years, 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 allowing them to learn to cook. Cooking meat eliminates pathogens and increases efficient protein digestion and nutritional value, paving the way for brain growth. The only problem with this hypothesis is a lack of data. Traditional methods have managed to find widespread evidence of fire use no older than 200,000 years, and only sparse evidence of controlled use of fire as long as 500,000 years ago. Only five archaeological sites around the world provide reliable evidence of ancient fire.

“We may have just found the sixth site,” says Dr. Natalio, whose previous collaboration with Dr. Azuri and colleagues provided the basis for this project. The two pioneered the application of AI and spectroscopy in archaeology to find indications of controlled burning of stone tools dating back to between 200,000 and 420,000 years ago in Israel. Now they’re back, joined by PhD student Zane Stepka, Dr. Liora Kolska Horwitz from the Hebrew University of Jerusalem and Prof. Michael Chazan from the University of Toronto, Canada.

The researchers’ “fishing” expedition began with the development of a more advanced AI model. With that in hand, the team could start fishing for molecular signals from the stone tools used by the inhabitants of the Evron Quarry site in northern Israel 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 (1,112°F). 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, not unlike the scientists themselves, were experimentalists.

According to the research team, by looking at the archaeological evidence from a different perspective, 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 hominins’ pyrotechnology-related behaviors evolved and drove other behaviors.

Dr. Filipe Natalio’s research is supported by the Artificial Intelligence and Smart Materials Research Fund, in Memory of Dr. Uriel Arnon; the Ilse Katz Institute for Material Sciences and Magnetic Resonance Research; and the Yeda-Sela Center for Basic Research.