He concluded, after studying rocks at many outcrops, that each layer represented a specific interval of geologic time.
Luminescence occurs in some minerals when they are exposed to low-powered sources of ultraviolet or infrared electromagnetic radiation (for example, portable UV lamps), at atmospheric pressure and atmospheric temperatures.
This property of these minerals can be used during the process of mineral identification at rock outcrops in the field, or in the laboratory.
Many advantages can be derived from such direct measurements of the metastable electron density in this particular trap, which produces the age-dependent signal.
The method can be used to date the last light exposure of feldspar grains within a range of a few hundred to more than 200,000 years.
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