The Complexity of ESR Signals in Tooth Enamel Fragments, A Comparison of Examples from Jebel Irhoud (Morocco) and Broken Hill (Zambia)

ABSTRACT This study presents the first comparative analysis of electron spin resonance (ESR) signal composition in fossil tooth enamel fragments from two key hominin sites: Jebel Irhoud (Morocco) and Broken Hill (Zambia). Using a simulated annealing decomposition method, we quantified the contributions of two major radical types, non‐oriented (NOCORs) and anisotropic (AICORs), to assess their impact on ESR dose estimation. NOCORs accounted for 8%–10% of the natural signal in Jebel Irhoud and 14%–15% in Broken Hill, rising significantly after gamma irradiation and leading to dose underestimation if not properly corrected. Differences in radical behavior and saturation responses between samples highlight the importance of site‐specific calibration in ESR dating. Our findings demonstrate the use of enamel fragments in ESR dating, which offer a reliable and minimally invasive alternative to conventional powder methods—particularly valuable when analyzing precious hominin fossils. The results also support the growing recognition that X‐ray irradiation in ESR dating protocols, shown in previous studies to generate no significant increase of unstable NOCORs, may provide a more effective option for equivalent dose ( D E ) determination without the need to correct for NOCORs. This work provides new insights into the complexity of ESR signals in teeth enamel. By addressing the impact of signal components like NOCORs, the study refines existing protocols and improves the ESR accuracy of chronologies in paleoanthropological research. Further methodological refinements will be essential to improve the accuracy of direct dating and ultimately enhance the chronologies of key early human evolution fossil specimens.