One might think that people who lived between 420,000 and 200,000 years ago were not very clever or advanced. But cutting-edge analyses by scientists at the Weizmann Institute of Science in Rehovot of stone tools from the Lower Paleolithic era in what became the Land of Israel have revealed that these early humans used very sophisticated techniques not only to create fire but also to make implements from stone.

The effects of heating the stone before flaking it into blades

According to research just published in the prestigious journal Nature Human Behavior, these ancient hominims (a group that includes modern man and the extinct members of our family tree) may have had a good understanding of the effects of heating the stone before flaking it into blades – and they may even have used different temperatures to create different types of tools. 

Qesem Cave is an archaeological site consisting of limestone located near the city of Kafr Qasim in the western mountain ridge of Israel between the Samaria Hills and the Israeli coastal plain. First found exactly 20 years ago when road construction destroyed its ceiling, the cave underwent two rescue excavations in 2001. At present the site is protected, covered and fenced and subject to on-going excavations by Prof. Avi Gopher and colleagues at Tel Aviv University. 

The hominims who lived in Qesem Cave left behind them tens of thousands of stone tools made mainly of flint, a material that is readily available all over the country. They were produced in a process called knapping –using another rock or tool to chip off pieces and honing a sharp edge. 

The main prey these hominins hunted had changed

Somewhere between 300,000 and 400,000 years ago, the main prey these hominins hunted had changed – from elephants to fallow deer – thus requiring a switch in their kitchen toolkit towards finer artifacts. The question asked by the Weizmann research group was whether the ancient inhabitants of the area might have used fire to temper the flint before knapping it. 

Less than 100,000 years ago, other groups had left evidence of firing their flint, which makes the stone easier to shape, but in sites of the Lower Paleolithic age, there has been almost no remaining organic matter that could give researchers conclusive evidence of the use of fire. 

Traces of past heating in solid rock would be mostly microscopic

The first challenge in trying to understand whether flint had undergone any structural change, such as fire can produce, explains Dr. Filipe Natalio of the Rehovot institute’s scientific archaeology Unit, 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. 

The traces of past heating in solid rock would be mostly microscopic or smaller – basically invisible. To overcome this hurdle, 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 and in 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. 

As the experiment yielded vast amounts of data – too large to analyze with regular methods, the group turned to Dr. Ido Azuri, who is in the institute’s bioinformatics unit in the life sciences core facilities department. 

This method could find the temperature range in which each had been heated

Since Azuri is an expert in machine learning and artificial intelligence and despite the departure from his normal biological research, he found patterns in large amounts of data that right up his alley. Indeed, he was delighted to find 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 that 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. 

Three different types of flint artifacts

 “At first,” recalled, Natalio, “the data seemed to be all over the place, and we didn’t know if we could say anything about these tools. But then Azuri created his model, and things just fell into place.” 

 A combined version of the findings compared three different types of flint artifacts, which 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. That indicated to the team that their analysis was on the right track, as very high heat – up to 600 degrees Celsius – had been suggested, in other studies, to create 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 (some 200 to 300 degrees Celsius – which are low-to-medium oven settings) and the temperature range they had undergone was much smaller. In other words, it appeared as though the cave’s inhabitants had intentionally used different heat-treatment s 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,” concluded Natalio. “And that,” added Pinkas, “is technology, as surely as our cellphones and computers are technology. It enabled our ancestors to survive and thrive.”