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Estimating temperatures of heated Lower Palaeolithic flint artefacts

A Publisher Correction to this article was published on 26 November 2020

This article has been updated

Abstract

Production of stone artefacts using pyro-technology is known from the Middle and Upper Palaeolithic of Europe and the Levant, and the Middle Stone Age in Africa. However, determination of temperatures to which flint artefacts were exposed is impeded by the chemical and structural variability of flint. Here we combine Raman spectroscopy and machine learning to build temperature-estimation models to infer the degree of pyro-technological control effected by inhabitants of the late Lower Palaeolithic (Acheulo-Yabrudian) site of Qesem Cave, Israel. Temperature estimation shows that blades were heated at lower median temperatures (259 °C) compared to flakes (413 °C), whereas heat-induced structural flint damage (for example, pot-lids and microcracks) appears at 447 °C. These results are consistent with a differential behaviour for selective tool production that can be viewed as part of a plethora of innovative and adaptive behaviours of Levantine hominins >300,000 years ago.

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Fig. 1: Road map for artificial intelligence applied to flint-based stone tools.
Fig. 2: Qesem Cave.
Fig. 3: Estimated temperatures of the artefacts analysed.
Fig. 4: ML estimation of QC artefacts collected along Deep Shelf Unit I.

Data availability

The raw UV Raman spectra are publicly available at https://github.com/fnatalio/QesemCave-UVRaman.

Code availability

The custom code supporting the findings of this study is available from the corresponding author upon request.

Change history

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Acknowledgements

We thank R. Barkai (Tel Aviv University, Israel) for his advice and help in conducting the blind flint knapping experiments. We thank V. Levy for her help in sample collection and Y. Avni (Geological Survey Israel) for his help in collecting flint from the Negev Desert. This work was supported by a research grant from the Benoziyo Endowment Fund for the Advancement of Science, Estate of Raymond Lapon and Estate of Olga Klein Astrachan and a research grant from the George Schwartzman Fund (Weizmann Institute of Science). I.P. is the incumbent of the Sharon Zuckerman Research Fellow Chair. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

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Authors

Contributions

A.A., I.A., I.P., A.G. and F.N. designed the study. QC excavations were carried out by A.G. A.A. and F.N. collected the geological samples. UV Raman measurements were conducted by A.A. and I.P. Machine learning analysis and temperature estimations were performed by I.A. Sediment sampling was carried out by A.A., A.G. and F.N. FTIR analysis was performed by F.N. Data analysis was conducted by A.A. and F.N. This manuscript was written and edited by A.A., I.A., I.P., A.G. and F.N. All authors commented on and contributed to the manuscript.

Corresponding author

Correspondence to Filipe Natalio.

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The authors declare no competing interests.

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Peer review information Primary handling editor: Charlotte Payne.

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Extended data

Extended Data Fig. 1 Raw flint collection locations.

Map displaying the locations from where the raw flint was collected (red dots).

Extended Data Fig. 2 Heat treatment of flint.

Photographic images of flint collected from different geological formations across Israel before and after heating to 275, 400, 500, 600, 700 and 800 °C for 3h. The samples were allowed to slowly cool down to room temperature. The samples were kept overnight inside the oven. Macroscopic visual evaluation of flint exposed to heat is not a reliable proxy for determining whether or not flint was heat-treated. Scale bar: 2 cm.

Extended Data Fig. 3 UV-Raman spectrum of flint.

Unprocessed UV Raman spectrum taken from a flint surface collected from Mor formation (Sde Boker, Negev Desert, Israel) using 325 nm wavelength. The spectrum obtained using UV laser (325 nm) shows no intrinsic autofluorescence.

Extended Data Fig. 4 Qesem Cave flakes.

Photographic images of all the flakes used in this study.

Extended Data Fig. 5 Qesem Cave blades.

Photographic images of all the blades used in this study.

Extended Data Fig. 6 Deep Shelf Unit I cross-section.

Photographic images from a freshly exposed Qesem Cave ‘Deep Shelf’ cross-section. The blue tags (Sed 1–20) show the locations from which 20 samples of sediment were taken. The deeper sediments (including ‘Deep Shelf Unit I’) comprise in situ almost horizontal deposits.

Extended Data Fig. 7 FT-IR analysis of sediments.

FT-IR spectra of the sediments (N=20) collected from the freshly exposed Qesem Cave ‘Deep Shelf Unit I’ cross-section. The main clay peak centers around 1032 cm-1 with the 3695 and 3620 cm-1 (clay structural water) peaks indicating that the sediment from where the artefacts were taken was not exposed to temperatures exceeding 400 °C. In addition, FT-IR analysis of splitting factor of bone1,2 and the absence of pyrogenic calcite3,4 in all sediments samples show that the bones were not burnt (Supplementary Figs. 9 and 10), and the calcite falls on the grinding curves of chalk (Supplementary Fig. 11), respectively. Taken together, these sediments were not exposed to heat supporting the idea that the artefacts were intentionally burnt in a location different from where they were unearthed.

Extended Data Fig. 8 Flint artefacts distribution.

Average of the estimated temperatures of artefacts (both blades and flakes) by sub-squares (of 1x1m square) of Deep Shelf Unit I. The data show no temperature-based clustering.

Supplementary information

Supplementary Information

Supplementary Note, Supplementary Figs. 1–13, Supplementary Table 1 and Supplementary References.

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Agam, A., Azuri, I., Pinkas, I. et al. Estimating temperatures of heated Lower Palaeolithic flint artefacts. Nat Hum Behav 5, 221–228 (2021). https://doi.org/10.1038/s41562-020-00955-z

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