Many materials found in archaeological sites are able to trap electronic charges as a result of bombardment by radioactive radiation from the surrounding sediment. The presence of these trapped charges can be detected by electron spin resonance (ESR) spectroscopy: the intensity of the ESR signal is a measure of the accumulated dose and thus of the age. Tooth enamel is ubiquitous at archaeological sites and is well suited for ESR dating, with a precision of about 10-20%. This method has now been used to date many sites critical to the biological and cultural evolution of modern man. Dates for sites in Israel and Africa have demonstrated the existence of anatomically modern humans more than 100 ka ago.