Photo Credit: Weizmann Institute of Science

Our ancestors, the first modern humans, knew how to use fire and developed sophisticated technologies for making tools, researchers at the Weizmann Institute of Science have recently discovered.

Employing, cutting-edge technologies to take a fresh look at a collection of stone tools, the Israeli team found 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 they may have used different temperatures to create different types of tools.

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The tools come from the Qesem Cave in Central Israel, which was excavated by Prof. Avi Gopher and his colleagues at Tel-Aviv University.

The findings in the cave that scientists date to between 420,000 and 200,000 years ago, or the Lower Paleolithic, and it is assigned to the unique Acheulo-Yabrudian Cultural Complex.

The ancient hominins who lived in the cave left behind tens of thousands of stone tools. These tools are mainly made of flint, a material which is available all over the country, and they were produced in a process called knapping –using another rock or tool to chip off pieces, honing a sharp edge.

Somewhere between 300,000-400,000 years ago, according to the researchers, the main prey these hominins hunted had changed from elephants to fallow deer, necessitating a switch in the 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. It is known that later groups, less than 100,000 years ago, had 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.

The first challenge in trying to understand whether flint had undergone any structural change produced by fire, explained Dr. Filipe Natalio of the Institute’s Scientific Archaeology Unit. The traces of past heating in solid rock would be mostly microscopic or smaller, basically invisible.

Tackling this challenge, 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’ spectroscopy lab, which revealed the makeup of these rocks down to their chemical and molecular structure.

The experiment yielded vast amounts of data, too large 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. Azuri is an expert in machine learning and artificial intelligence, so finding patterns in large amounts of data was right up his alley.

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 this method could also 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.

Azuri then 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.

A distilled version of the findings compared three different types of flint artifacts, and it 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.

The second type of pieces are known as flakes; and the third is 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.

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,” said Natalio.

“That is technology, as surely as our cell phones and computers are technology. It enabled our ancestors to survive and thrive,” added Pinkas.

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