ArchaeologySecond study at site finds ash used as a preservative

Cave dwellers forged their tools in fire 300,000 years ago, Israeli study shows

Weizmann Institute findings based on AI analysis of flint from Qesem Cave, using tool-making re-enactment, hi-tech Raman spectroscopy, and machine learning

Amanda Borschel-Dan is The Times of Israel's Jewish World and Archaeology editor.

Dr. Filipe Natalio, seen here at a site in the Negev Desert, holding a flint tool. (screenshot)
Dr. Filipe Natalio, seen here at a site in the Negev Desert, holding a flint tool. (screenshot)

Ancient man harnessed the power of fire to skillfully forge specific stone tools, some 300,000 years ago, according to a new study from researchers at the Weizmann Institute of Science.

“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 Dr. Filipe Natalio of the Institute’s Scientific Archaeology Unit in a press release.

The interdisciplinary team of Weizmann scientists opened their study — published Monday in the prestigious Nature Human Behaviour journal — with the question of whether a now-extinct branch of humanity that had lived in central Israel’s Qesem Cave adapted their tool making skills as their diet changed 300,000-400,000 years ago.

The many generations of Lower Paleolithic cave dwellers, whose residence spanned from 420,000 and 200,000 years ago, left behind tens of thousands of flint tools, some of which were excavated by Tel Aviv University’s Prof. Avi Gopher. As the residents’ diets changed from large prey such as elephants, to fallow deer, the Weizmann researchers wondered, did they adopt the technique of firing stone to temper the flint before knapping it into finer slices.

The Qesem Cave excavation site, near Rosh Haayin in central Israel, December 29, 2010. (AFP/Jack Guez/File)

According to a Weizmann press release, Natalio of the Institute’s Scientific Archaeology Unit, postdoctoral fellow Dr. Aviad Agam, and Dr. Iddo Pinkas, who is an expert in a technique known as Raman spectroscopy in the Institute’s Chemical Research Support Department, decided to conduct an experiment. They collected flint from several Israeli locations, including the Qesem Cave. The researchers heated and cooled the rocks, then examined their chemical and molecular structure.

Slightly derailed by an avalanche of data, the team turned to an expert in machine learning and artificial intelligence, Dr. Ido Azuri, who is part of the Weizmann Bioinformatics Unit. Together, the scientists were able to sift the information and discern the changes caused by baking the rocks. Through the machine learning, they were also able to discover the temperature range in which each tool was heated and created a stratified model.

The researchers then studied Gopher’s ancient samples from Qesem Cave and attempted to figure out the temperatures to which ancient man heated the flints, through Azuri’s model.

Left-to-right (not to scale): A pot-lid, flake and blade. Each was produced at a different temperature (courtesy of the Weizmann Institute of Science)

“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 in the press release.

The scientists compared three types of flint artifacts, which, it was revealed, were fired at three different temperature ranges according to tool type. The small flint “pot-lids,” were nicked and chipped shards. Spectroscopy and AI analysis indicated that during firing, the flint pieces were dislodged by the heat of up to 600 degrees Celsius. Small cutting tools, “flakes,” on the other hand, were fired to a large temperature range of temperatures.

The third group of tools, labeled “blades,” were long tools with one sharp edge and an opposite, thicker dull side for gripping. The scientists found that the blades were heated at a smaller temperature range and at relatively lower temperatures (some 200-300 degrees).

A comparison of temperatures for three types of tool reveals a small, relatively cool range for blades, in contrast with the other two. (courtesy, the Weizmann Institute of Science)

The scientists concluded that this ability to harness fire to create better adapted tools was intentional.

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

First use of ash as food preservative in Late Lower Paleolithic

A separate analysis of Qesem Cave findings published in September in the prestigious PLOS journal identifies the earliest use of ash in food cooking and storage, as well as the treatment of hide.

Qesem Cave seems to provide the earliest evidence related to the utilization of ash for storing and processing vegetal foods

“Qesem Cave seems to provide the earliest evidence related to the utilization of ash for storing and processing vegetal foods and hide linked to the outstanding preservation properties of ash,” write the authors.

The team of Italian researchers from Sapienza University implement use-wear and residue analyses, controlled experiments, and a corroborating blind test, according to the study, “The use of ash at Late Lower Paleolithic Qesem Cave, Israel—An integrated study of use-wear and residue analysis.”

“Our current findings present evidence for the processing of organic matters intentionally mixed with ash, leading us to suggest that the inhabitants of Qesem Cave were proficient not only in the habitual use of fire, but also of its main by-product, ash,” write the authors.

The impetus of the study came when the researchers noticed a fine polish on some of the flint tools from Qesem. Fine ash was readily available in the archaeological site, giving the researchers a powdery possibility.

“We thought that the brightness of the polish, and the tight linkage between polish and the striations suggest that animal and plant processing activities achieved with these tools involved some unknown abrasive powdery component that had the power to enhance the degree of leveling of the micro-surface of the used flint tools while also slightly grazing their surface,” they write.

Experiment: a) peeling and cutting fresh asphodel; b) peeling and cutting fresh asphodel in ashy environment presence of ash (blind test); c) peeling roasted cyclamen; d) cleaning off subcutis of fresh hide (blind test); e) cleaning off subcutis of fresh hide in ashy environment (blind test); f) cutting dry hide preserved in ash. (Courtesy PLOS/

The scientists also noted a morphological similarity to results from hide-working experiments they had conducted in which hide was preserved in cold ashes before tanning. In addition, their onsite experiments have shown that ash aids in the preservation of dry untanned hides; for preserving drying tendons that can be turned into strings; and for drying fresh bone to easily remove fleshy tissues ahead of producing bone tools.

The researchers note that worldwide, ash was used for four main purposes: food roasting and cooking; preservation of edible matters, such as dried food, or of fresh hides; hygiene treatments against bugs and parasites; and medicinal uses.

In the Qesem Cave sample specifically, the scientists did not find indications of all four ash usages. Their results do indicate, however, that underground storage organs and other plants “were probably roasted or preserved (in ash) for delayed consumption, and that ash appears to have been used for treating and preserving raw hide. This suggests that the site’s inhabitants had already mastered the outstanding properties of ash for roasting/cooking and preservation purposes.”

Similar to the Weizmann researchers, the Italian study concludes that the use of fire and ash was highly intentional.

“Our results highlight the possibility that fire was used purposefully and indirectly (as opposed to its direct uses of heat, light, and security) in the Levant from ca. 300 kya onwards through the utilization of its by-product, ash,” they write.

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