Periodic Reporting for period 1 - WATIME (West African Middle Stone Age Timeline using ESR dating of quartz)
Période du rapport: 2023-10-01 au 2025-09-30
The WATIME project, hosted at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH, Spain), focused on improving the accuracy of dating methods used to build the chronology of the Middle Stone Age (MSA) in western Africa. Dating archaeological sites in this region remains a major challenge, as conventional methods such as radiocarbon or argon-argon dating cannot be applied due to the absence of suitable materials such as bones, charcoal, shells, or volcanic minerals.
Quartz, however, is a common mineral present everywhere and represents an excellent candidate for dating using trapped-charge techniques such as Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR). Until now, OSL has been almost exclusively used as the main alternative dating technique to establish the chronology of western African Stone Age sites. However, this method presents clear limitations: it cannot be extended beyond approximately 150,000 years and is therefore unable to cover the full temporal range of the MSA.
Before 2021, the earliest evidence of human occupation in western Africa was dated to ca. 130,000 years ago. Earlier occupations were unknown, leaving a major chronological gap in our understanding of the presence and adaptation of early Homo sapiens in this region. The main objective of WATIME was to refine and enhance the precision of the ESR dating method applied to quartz grains, in order to overcome the limitations of OSL and provide the first robust chronological framework for key MSA sites across western Africa. The project also tests the potential of ESR to push back the antiquity of human presence in the region by applying this method to key archaeological sites defined as early to late MSA. This approach makes it possible to extend the dating range beyond that achievable by OSL (Middle–Early Late Pleistocene), thereby shedding new light on the timing, environmental context, and behavioural evolution of early human populations, mainly in tropical and coastal western Africa.
Quartz, however, is a common mineral present everywhere and represents an excellent candidate for dating using trapped-charge techniques such as Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR). Until now, OSL has been almost exclusively used as the main alternative dating technique to establish the chronology of western African Stone Age sites. However, this method presents clear limitations: it cannot be extended beyond approximately 150,000 years and is therefore unable to cover the full temporal range of the MSA.
Before 2021, the earliest evidence of human occupation in western Africa was dated to ca. 130,000 years ago. Earlier occupations were unknown, leaving a major chronological gap in our understanding of the presence and adaptation of early Homo sapiens in this region. The main objective of WATIME was to refine and enhance the precision of the ESR dating method applied to quartz grains, in order to overcome the limitations of OSL and provide the first robust chronological framework for key MSA sites across western Africa. The project also tests the potential of ESR to push back the antiquity of human presence in the region by applying this method to key archaeological sites defined as early to late MSA. This approach makes it possible to extend the dating range beyond that achievable by OSL (Middle–Early Late Pleistocene), thereby shedding new light on the timing, environmental context, and behavioural evolution of early human populations, mainly in tropical and coastal western Africa.
During the two-year Marie Skłodowska-Curie Fellowship (2023–2025), the fellow carried out an extensive programme of fieldwork, laboratory analyses, and methodological developments in ESR dating. Fieldwork missions in Senegal and Ghana provided new quartz samples for supplementary dating. More than 30 samples from 24 Stone Age sites were analysed across diverse depositional environments.
Laboratory work was conducted mainly at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH, Spain), leveraging its state-of-the-art ESR facilities, including two X-band ESR spectrometers (EMX and ELEXSYS) at low temperature using a nitrogen cooling system. Complementary OSL analyses were performed in collaboration with the OSL laboratory at CENIEH. Additional ESR experiments were performed at the Leibniz Institute for Applied Geophysics (LIAG, Hannover, Germany) to implement and test the Single Aliquot Regenerative (SAR) protocol, using an X-band ESR spectrometer (ELEXSYS) at low temperature with a nitrogen cooling system and employing a heating system and X-ray irradiators. Together, these activities enabled the fellow to test, optimise, and validate ESR protocols across a wide range of depositional and taphonomic contexts in western Africa, providing robust methodological developments and reliable chronological results for Middle Stone Age sites. Key technical and scientific results were achieved and are summarised below:
1. Improving the accuracy of ESR dating methods through optimisation of experimental protocols
The project focused on improving ESR dating on quartz grains. Working with quartz from western Africa proved challenging because the chronological signals were often very weak. The fellow developed a new detection protocol, the “Twin Windows” method, which enhances signal clarity and allows for more reliable age measurements. This method was first tested on samples from Côte d’Ivoire. Additionally, many samples displayed noisy or distorted signals that made age estimates uncertain. A new correction procedure was therefore developed to remove background noise and adjust the data, leading to more accurate equivalent dose determinations (one of the key parameters used to calculate ESR ages).
2. Modern analogue correction model
A model was developed to adjust ESR ages by comparing them with modern samples. In some western African sites, quartz grains were not fully reset before their deposition, leaving a residual dose that can represent up to 30% of the natural signal. By subtracting this residual dose, ESR ages show better agreement with OSL dating results. This correction helps explain why some ESR ages appeared too old—particularly in sites with fluvial or colluvial deposits.
3. Describing the behaviour of quartz during irradiation
The Single Saturating Exponential (SSE) function, when applied to the initial data points, provides the best description of signal evolution with increasing dose, producing ESR ages closely matching OSL ages. This represents a methodological advance in modelling dose–response curves and ensures greater consistency between ESR and OSL chronologies.
4. Testing and comparing ESR dating procedures
Two main ESR approaches were tested: the traditional Multiple Aliquot Additive Dose (MAAD) method and the Single Aliquot Regenerative (SAR) method. While the traditional MAAD method gave consistent results with OSL dating in many cases, it is less precise for very old samples (between 400,000 and 100,000 years), whereas the SAR method, tested in a few samples from Senegal, produced more precise results. The choice of ESR dating procedure must be adapted to the site type and its geological conditions.
5. Evaluation of ESR performance across different depositional contexts
The performance of ESR dating was evaluated under a range of environmental conditions. Under ideal conditions—such as well-bleached coastal deposits along the western coast of Senegal—MAAD yields results consistent with OSL. However, in less favourable contexts, such as fluvial deposits in Côte d’Ivoire or Guinea, uncertainties in equivalent dose and age estimates can reach up to 36%. These findings highlight the importance of considering depositional history and bleaching conditions when interpreting ESR ages.
6. Dating applications across diverse environments
The methodological developments were applied to a large regional dataset covering approximately 20 Stone Age sites across Senegal, Côte d’Ivoire, Guinea, and Mali, as well as new collections from four additional MSA sites in Senegal and Ghana. These sites represent a wide range of depositional environments, including coastal, fluvial, tropical forest, and inland Sahelian contexts. Among the 20 targeted sites (plus four new MSA sites), 16 yielded exploitable ESR results—representing a 75% success rate. This demonstrates the strong potential of the refined ESR protocols for obtaining reliable chronologies across diverse geomorphological and taphonomic settings in West Africa.
Laboratory work was conducted mainly at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH, Spain), leveraging its state-of-the-art ESR facilities, including two X-band ESR spectrometers (EMX and ELEXSYS) at low temperature using a nitrogen cooling system. Complementary OSL analyses were performed in collaboration with the OSL laboratory at CENIEH. Additional ESR experiments were performed at the Leibniz Institute for Applied Geophysics (LIAG, Hannover, Germany) to implement and test the Single Aliquot Regenerative (SAR) protocol, using an X-band ESR spectrometer (ELEXSYS) at low temperature with a nitrogen cooling system and employing a heating system and X-ray irradiators. Together, these activities enabled the fellow to test, optimise, and validate ESR protocols across a wide range of depositional and taphonomic contexts in western Africa, providing robust methodological developments and reliable chronological results for Middle Stone Age sites. Key technical and scientific results were achieved and are summarised below:
1. Improving the accuracy of ESR dating methods through optimisation of experimental protocols
The project focused on improving ESR dating on quartz grains. Working with quartz from western Africa proved challenging because the chronological signals were often very weak. The fellow developed a new detection protocol, the “Twin Windows” method, which enhances signal clarity and allows for more reliable age measurements. This method was first tested on samples from Côte d’Ivoire. Additionally, many samples displayed noisy or distorted signals that made age estimates uncertain. A new correction procedure was therefore developed to remove background noise and adjust the data, leading to more accurate equivalent dose determinations (one of the key parameters used to calculate ESR ages).
2. Modern analogue correction model
A model was developed to adjust ESR ages by comparing them with modern samples. In some western African sites, quartz grains were not fully reset before their deposition, leaving a residual dose that can represent up to 30% of the natural signal. By subtracting this residual dose, ESR ages show better agreement with OSL dating results. This correction helps explain why some ESR ages appeared too old—particularly in sites with fluvial or colluvial deposits.
3. Describing the behaviour of quartz during irradiation
The Single Saturating Exponential (SSE) function, when applied to the initial data points, provides the best description of signal evolution with increasing dose, producing ESR ages closely matching OSL ages. This represents a methodological advance in modelling dose–response curves and ensures greater consistency between ESR and OSL chronologies.
4. Testing and comparing ESR dating procedures
Two main ESR approaches were tested: the traditional Multiple Aliquot Additive Dose (MAAD) method and the Single Aliquot Regenerative (SAR) method. While the traditional MAAD method gave consistent results with OSL dating in many cases, it is less precise for very old samples (between 400,000 and 100,000 years), whereas the SAR method, tested in a few samples from Senegal, produced more precise results. The choice of ESR dating procedure must be adapted to the site type and its geological conditions.
5. Evaluation of ESR performance across different depositional contexts
The performance of ESR dating was evaluated under a range of environmental conditions. Under ideal conditions—such as well-bleached coastal deposits along the western coast of Senegal—MAAD yields results consistent with OSL. However, in less favourable contexts, such as fluvial deposits in Côte d’Ivoire or Guinea, uncertainties in equivalent dose and age estimates can reach up to 36%. These findings highlight the importance of considering depositional history and bleaching conditions when interpreting ESR ages.
6. Dating applications across diverse environments
The methodological developments were applied to a large regional dataset covering approximately 20 Stone Age sites across Senegal, Côte d’Ivoire, Guinea, and Mali, as well as new collections from four additional MSA sites in Senegal and Ghana. These sites represent a wide range of depositional environments, including coastal, fluvial, tropical forest, and inland Sahelian contexts. Among the 20 targeted sites (plus four new MSA sites), 16 yielded exploitable ESR results—representing a 75% success rate. This demonstrates the strong potential of the refined ESR protocols for obtaining reliable chronologies across diverse geomorphological and taphonomic settings in West Africa.
The investigations carried out during the WATIME project have led to major impacts.
Scientific and methodological advances: WATIME has developed and refined new analytical procedures that substantially improve the reliability of ESR dose estimations in quartz grains—addressing one of the central challenges in trapped-charge dating. This pioneering work, validated through publications in Nature, Quaternary Environments and Humans, Ancient TL, and Radiation Physics and Chemistry, represents the first systematic integration of ESR and OSL dating methods applied to Stone Age sites in West Africa, and more broadly across Africa.
These advances enable ESR to be applied to the same quartz grains as OSL, making it possible to cross-validate age estimates, identify signal discrepancies, and improve chronological precision. The integration of the two techniques provides a multi-dating framework that strengthens chronological reliability and reveals the underlying processes driving divergence between methods—an essential step toward refining human evolutionary models.
Chronological and archaeological breakthroughs: The project has generated the first direct ages for human occupation in tropical forest environments not only in Africa but worldwide, dating a site in Côte d’Ivoire to approximately 150,000 years ago, and establishing the earliest Middle Stone Age evidence in West Africa at around 140,000 years ago, in association with mangrove environments. These results, published in Nature, demonstrate that human populations occupied tropical ecosystems much earlier than previously believed (~18 ka), requiring a significant revision of existing models of ecological adaptation and human dispersal.
Several additional papers in preparation will provide new paired ESR–OSL chronologies for the early Middle Stone Age in West Africa, further illuminating the timing and environmental diversity of Homo sapiens emergence. By demonstrating the feasibility of ESR dating in tropical contexts and extending the chronological range, WATIME opens new avenues for understanding early human evolution across Africa.
Societal and scientific impacts: Beyond its immediate scientific contributions, WATIME highlights the high potential of West African archaeological sites for future chronological and interdisciplinary research. The project contributes to restoring their central role in narratives of human origins, which have historically been dominated by East and Southern African records. The publications and the data generated are made available through open-access repositories (e.g. CENIEH, HAL), fostering reuse and reproducibility.
The methodological and conceptual advances achieved through WATIME provide a robust foundation for future interdisciplinary studies linking geochronology, palaeoenvironmental reconstruction, and evolutionary anthropology. In doing so, the project contributes to building a more comprehensive, pan-African framework for understanding the deep-time history of our species.
Scientific and methodological advances: WATIME has developed and refined new analytical procedures that substantially improve the reliability of ESR dose estimations in quartz grains—addressing one of the central challenges in trapped-charge dating. This pioneering work, validated through publications in Nature, Quaternary Environments and Humans, Ancient TL, and Radiation Physics and Chemistry, represents the first systematic integration of ESR and OSL dating methods applied to Stone Age sites in West Africa, and more broadly across Africa.
These advances enable ESR to be applied to the same quartz grains as OSL, making it possible to cross-validate age estimates, identify signal discrepancies, and improve chronological precision. The integration of the two techniques provides a multi-dating framework that strengthens chronological reliability and reveals the underlying processes driving divergence between methods—an essential step toward refining human evolutionary models.
Chronological and archaeological breakthroughs: The project has generated the first direct ages for human occupation in tropical forest environments not only in Africa but worldwide, dating a site in Côte d’Ivoire to approximately 150,000 years ago, and establishing the earliest Middle Stone Age evidence in West Africa at around 140,000 years ago, in association with mangrove environments. These results, published in Nature, demonstrate that human populations occupied tropical ecosystems much earlier than previously believed (~18 ka), requiring a significant revision of existing models of ecological adaptation and human dispersal.
Several additional papers in preparation will provide new paired ESR–OSL chronologies for the early Middle Stone Age in West Africa, further illuminating the timing and environmental diversity of Homo sapiens emergence. By demonstrating the feasibility of ESR dating in tropical contexts and extending the chronological range, WATIME opens new avenues for understanding early human evolution across Africa.
Societal and scientific impacts: Beyond its immediate scientific contributions, WATIME highlights the high potential of West African archaeological sites for future chronological and interdisciplinary research. The project contributes to restoring their central role in narratives of human origins, which have historically been dominated by East and Southern African records. The publications and the data generated are made available through open-access repositories (e.g. CENIEH, HAL), fostering reuse and reproducibility.
The methodological and conceptual advances achieved through WATIME provide a robust foundation for future interdisciplinary studies linking geochronology, palaeoenvironmental reconstruction, and evolutionary anthropology. In doing so, the project contributes to building a more comprehensive, pan-African framework for understanding the deep-time history of our species.