Electron spin resonance (ESR) can be used to determine the thermal history of charred organic material. Maize seeds were heated under controlled conditions in order to produce calibration curves relating g-values (the rate of electron splitting) and spin intensities (the number of spin centres) to heating temperatures, times and conditions. These experiments reproduced results that had been previously obtained by other laboratories, with some minor exceptions. The calibration curves were then used to reconstruct the thermal histories of charred maize kernels from several prehistoric sites in eastern North America. At these sites, the differing thermal histories of maize kernels are correlated with depositional contexts.
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