Luminescence Dating

Luminescence dating encompasses a range of methods that seek to determine when mineral grains were last exposed to sunlight or heat.

Taking the Sediments to the Lab

In the wet chemistry lab, sand-sized grains of two minerals (quartz and potassium feldspar) are separated out from the sediment and purified. The mineral grains are then placed on to metal discs and loaded into a machine that has a photomultiplier tube, a radiation source, and a light source to optically stimulate the grains (e.g. light emitting diodes or lasers). Light is shone onto the quartz and feldspar grains and the photomultiplier tube detects the light given off by the minerals, using filters to select a different colour from the stimulating light source. This helps to identify how much radiation has been stored in the same grains since they were buried in the ground. Together with measurements of how much radiation the grains received each year in the ground, the time of burial of the grains can be determined. This information can answer the following questions:

• How long ago were the sediment grains buried in the ground?
• How old are the artefacts and fossils associated with that sample of sediment or sediment layer?
• Are there any indications of sediment disturbances after burial that might need to be taken into account?

Currently, experts are applying dating techniques to samples from Liang Bua to identify the first time that modern humans stepped foot in the cave.