Trapped methyl radicals in chert

We have demonstrated recently that electron spin resonance (ESR) spectroscopy can detect a narrow signal from electron gain (E′) centres in flint (Upper Cretaceous lepispheric chert)1. This signal, caused by the effect of natural radiation, is lost on heating and may be useful for dating2. ESR signals from various organic radicals are now reported in a wide variety of cherts. The thermal dependence of the signals may provide valuable information about the duration and temperature of ancient chert heatings.