Israeli study finds ancient hominins used fire to make tools

The findings from the cave have been dated to between 420,000 and 200,000 years ago, or the Lower Paleolithic period.

A pot-lid, flake and blade (not to scale). Each was produced at a different temperature. (photo credit: WEIZMANN INSTITUTE OF SCIENCE)
A pot-lid, flake and blade (not to scale). Each was produced at a different temperature.
In an article that appeared Monday in Nature Human Behaviour, researchers at the Weizmann Institute of Science in Rehovot detail how they employed cutting-edge technologies to take a fresh look at a collection of ancient stone tools. Their results suggest that the early humans who made them may have had a good understanding of the effects of heating the stone before flaking it into blades and may even have used a variety of temperatures to create different types of tools.
Qesem Cave, a site in central Israel, was excavated by Prof. Avi Gopher and colleagues at Tel Aviv University, and the findings from the cave have been dated to between 420,000 and 200,000 years ago – the Lower Paleolithic period – and it is assigned to the unique Acheulo-Yabrudian Cultural Complex.
The ancient hominins, a group that includes modern humans as well as extinct human species, who lived in Qesem Cave, left behind tens of thousands of stone tools. These tools are mainly made of flint, a material which is readily available all over the country, and they were produced in a process called knapping, a process that uses another rock or tool to chip off pieces, honing a sharp edge. Somewhere between 300,000-400,000 years ago, the main prey these hominins hunted changed from elephants to fallow deer, which meant that they had to change and refine the tools they used to hunt. The Weizmann research group examined the question of whether the ancient inhabitants of the area might have used fire to temper the flint before knapping it. Much later groups – less than 100,000 years ago — left evidence of firing their flint, which makes the stone easier to shape. However, in sites of this age, there is generally almost no remaining organic matter that can give researchers conclusive evidence of fire use.
According to Dr. Filipe Natalio of Weizmann’s Scientific Archaeology Unit, the first challenge in trying to understand whether flint has undergone any structural change that could indicate it had been heated by fire, is that the structure of raw flint can vary from site to site and from piece to piece, depending on the geological conditions in which it formed. And the traces of past heating in solid rock would be mostly microscopic or smaller – basically invisible. He and postdoctoral fellow Dr. Aviad Agam, who specializes in prehistoric archaeology, turned to Dr. Iddo Pinkas, who is an expert in a technique known as Raman spectroscopy in the Institute’s Chemical Research Support Department.
The group first collected flint from areas near Qesem Cave as well as other places around the country. After heating the flint pieces to different temperatures and cooling them again, the researchers examined them with the tools in Pinkas’s spectroscopy lab, which revealed the makeup of these rocks down to their chemical and molecular structure.
The experiment yielded vast amounts of data – too much to analyze with regular methods. So the group turned to Dr. Ido Azuri, who is in the Institute’s Bioinformatics Unit, in the Life Sciences Core Facilities Department, and is an expert in machine learning and artificial intelligence. He found that not only could the spectroscopy data be analyzed through machine learning methods, so as to sort out the changes caused by baking the rocks, but this method could find the temperature range in which each had been heated.
Next, the group applied the spectroscopy and AI analysis to randomly chosen samples from the thousands of pieces of ancient knapped flint excavated from Qesem Cave by Gopher. Azuri took this new data and evaluated the temperatures to which the early humans heated the ancient knapped flints by the model he had originally created.
“At first, the data seemed to be all over the place, and we did not know if we could say anything about these tools. But then Azuri created his model, and things just fell into place,” said Natalio.
They compared three different types of flint artifacts, and revealed three unique temperature ranges, one for each kind. The first type, which the scientists call “pot-lids,” were small, nicked and chipped shards, and the analysis showed they had been exposed to fire hot enough to cause pieces of the flint to fly off on their own accord. That told the team their analysis was on the right track, as it had been suggested in other studies that very high heat – up to 600 degrees Celsius – had been suggested, created the nicks and chips. The second type of pieces are known as flakes and the third are the blades, larger, knife-like tools with one long sharp edge and a facing, thicker edge where they can be held. Flakes, essentially smaller cutting tools than the blades, had been treated at a relatively large range of temperatures while the blades had been heated to lower temperatures and the temperature range they had undergone was much smaller. In other words, it appeared as though the cave’s inhabitants had inten
tionally used different heat treatments to create different tools.
“We can’t know how they taught others the skill of toolmaking, what experience led them to heat the raw flint to different temperatures, or how they managed to control the process, but the fact that the longer blades are consistently heated in a different way than the other pieces does point to an intent,” said Natalio.
Pinkas said, “And that is technology, as surely as our cell phones and computers are technology. It enabled our ancestors to survive and thrive.”