The heat is on: Weizmann Institute scientists

They say that where there is smoke, there is fire, and researchers at the Weizmann Institute of Science are working hard to investigate this claim, or at least to elucidate what constitutes “smoke”. In an article published today in PNAS, scientists reveal an advanced and innovative method they developed and used to detect non-visual traces of fire dating back at least 800,000 years – one of the earliest known evidence of the use of fire. The newly developed technique may provide an impetus towards a more scientific and data-driven type of archaeology, but – perhaps more importantly – it could help us better understand the origins of human history, our deepest traditions. fundamentals and our experimental and innovative nature.

The controlled use of fire by ancient hominids – a group that includes humans and some extinct members of our family – is believed to date back at least a million years, around the time archaeologists believe Homo habilis began its transition to homo erectus. This is no coincidence, as the working theory, called the “cooking hypothesis”, is that the use of fire has been instrumental in our evolution, not just for keeping hominids warm , to make advanced tools and ward off predators, but also to acquire the ability to cook. Cooking meat not only eliminates pathogens, but increases protein digestion efficiency and nutritional value, paving the way for brain growth. The only problem with this hypothesis is the lack of data: since the search for archaeological evidence of pyrotechnology relies mainly on the visual identification of the modifications resulting from the combustion of objects (mainly, a change in color), the methods traditional have managed to find widespread evidence of the use of fire. no more than 200,000 years old. While there is some evidence of a fire dating back 500,000 years ago remains scarce, with only five archaeological sites worldwide providing reliable evidence of an ancient fire.

“We may have just found the sixth site,” says Dr. Filipe Natalio of Weizmann’s Department of Plant and Environmental Sciences, whose previous collaboration with Dr. Ido Azuri of Weizmann’s Department of Vital Facilities and colleagues has served as the basis for this project. Together they pioneered the application of AI and spectroscopy in archeology to find evidence of the controlled burning of stone tools dating to between 200,000 and 420,000 years ago in Israel. They are now back, joined by PhD student Zane Stepka, Dr Liora Kolska Horwitz from the Hebrew University of Jerusalem and Professor Michael Chazan from the University of Toronto, Canada. The team upped the ante by organizing a “fishing expedition” – casting deep in the water and seeing what they could come up with. “When we launched this project, explains Natalio, the archaeologists who analyzed the Evron Quarry discoveries told us that we would find nothing. We should have made a bet.

The Evron Quarry, located in the Western Galilee, is an open-air archaeological site that was first discovered in the mid-1970s. During a series of excavations that took place at that time and were Led by Professor Avraham Ronen, archaeologists dug 14 meters and uncovered a wide range of Paleolithic animal and tool fossils dating from 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 visual evidence of heat: ashes and charcoal degrade over time, eliminating the chance of finding visual evidence of combustion. So if the Weizmann scientists wanted to find evidence of fire, they had to look further.

The “fishing” expedition began with the development of a more advanced AI model than the one they had used before. “We tested a variety of methods, including traditional data analysis methods, machine learning modeling and more advanced deep learning models,” says Azuri, who led the development of the models. “Prevailing deep learning models had a specific architecture that outperformed others and successfully gave us the confidence we needed to use this tool more in an archaeological context without visual signs of fire use.” The advantage of AI is that it can find hidden patterns across a multitude of scales. By identifying the chemical composition of materials down to the molecular level, the model’s output can estimate the temperature to which stone tools were heated, ultimately providing information about past human behaviors.

With an accurate AI method in hand, the team was able to begin fishing for molecular signals from the stone tools used by the inhabitants of the Evron Quarry nearly a million years ago. To that end, the team assessed the heat exposure of 26 flint tools found at the site nearly half a century ago. The results revealed that the tools had been heated to a wide range of temperatures – some exceeding 600°C. Additionally, using a different spectroscopic technique, they analyzed 87 faunal remains and found that an extinct elephant’s tusk also exhibited structural changes as a result of heating. Although cautious in their assertion, the presence of hidden heat suggests that our ancient ancestors, much like the scientists themselves, were experimenters.

According to the research team, by looking at archeology from a different perspective, using new tools, we could find much more than we initially thought. The methods they developed could be applied, for example, to other Lower Paleolithic sites to identify non-visual evidence of the use of fire. Additionally, this method could perhaps offer a renewed spatio-temporal perspective on the origins and controlled use of fire, helping us better understand how hominin pyrotechnology-related behaviors evolved and drove other behaviors. . “Especially in the case of an early fire,” explains Stepka, “if we use this method on archaeological sites that are one or two million years old, we might learn something new.”

By all accounts, the fishing expedition was a resounding success. “It was not just a demonstration of exploration and being rewarded in terms of the knowledge acquired”, explains Natalio, “but of the potential that lies in the combination of different disciplines: Ido has a background in quantum chemistry, Zane is a scientific archaeologist and Liora and Michael are prehistorians. Working together, we have learned from each other. To me, this is a demonstration of how scientific research in the humanities and science should work.

Dr. Natalio’s research is supported by the Yeda-Sela Basic Research Center.


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