ESR DATING IN THE 21st CENTURY: FROM BURIED VALLEYS AND DESERTS TO THE DEEP OCEAN AND OUTER SPACE

Electron spin resonance (ESR) dating can date many materials, including hydroxyapatite in enamel and some fish scales, aragonite and calcite in corals, molluscs, some travertine and calcrete, and quartz from ash, which have many potential applications in a wide variety of Quaternary settings and for dosimetry. ESR dating uses signals resulting from trapped charges created by radiation in crystalline solids. Ages are calculated by comparing the accumulated dose in the dating sample with the internal and external radiation dose rates produced by natural radiation in and around the sample and produced by cosmic radiation. Although the complexity of the signals in some materials, such as travertine, has hampered its routine application, research is solving these problems to make the method even more widely applicable. When tested against other dating techniques, age agreement has been excellent. Recent improvements have included using a more complex modelling technique to calculate the cosmic dose rates and more detailed modelling techniques for dealing with variable external dose rates. New chronometer applications recently developed include using the signals in barnacles, benthic foraminifera, coralline algae, and bryozoans for dating fossils or their associated sediment or archaeological materials. Mollusc and coral signals have recently be used to date volcanic deposits, to determine uplift rates for tectonically active coastlines, to develop sealevel curves in the Bahamas, and the date potential occupations in the Sahara. At least one lab is testing ostrich egg shell for its utility as a chronometer. In addition to being used to date fault activity, quartz and feldspar are both being examined for potential uses in dating Pleistocene buried valleys. Signals in quartz have also been used to determine the temperatures to which hominid artefacts have been heated. Possible extraterrestrial uses include dating sulphate and other minerals on distant planets.