Optically stimulated luminescence dating
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Optically Stimulated Luminescence or OSL Dating is a method of establishing the age of soil sediments. It is used by archaeologists or earth scientists as an alternative, or in addition to radiocarbon dating.
All soils contain trace minerals including uranium, thorium and potassium. These slowly decay over time and the ionising radiation they produce is absorbed by other constituents of the soil sediments such as quartz and feldspar. Stimulating samples using either blue or infrared light causes the luminescence signal to be emitted, the intensity of which varies depending on the amount of radiation absorbed during burial. Exposure to sunlight resets the luminescence signal and so the time period since the soil was buried can be calculated.
Wind blown and colluvial deposits are particularly suitable for dating using this method as it can be certain that those soils were exposed to sunlight before being overlain. As the technique does not require organic samples it is more widely applicable than carbon dating. It is also reliable over a longer period than C14 and can be used on deposits up to 200,000 years old. OSL is therefore most commonly used on prehistoric sites.