Some materials can trap invisible energy called radiation. Measuring how much energy is trapped can show how long this material has been buried in the ground. It can also show when something was burnt in a fire or heated to very high temperatures. Radiation is all around us. It can pass through most materials. However a group of materials called minerals can trap this energy. These minerals can be found in the soil, on the beach and in stone. Only after they are buried in the ground or have been in a fire do they start to capture radiation.

To work out how long ago this happened all a scientist has to do is to work out how much radiation is trapped and divide this by how much radiation is captured each year. Releasing the trapped radiation is simple. The material has to be reheated or exposed to sunlight. This produces a burst of light called luminescence. How bright the light is depends on how much energy has been trapped in the mineral – just like a battery-powered torch.

Anything containing the minerals that trap the radiation, such as quartz and feldspar, can be dated in this way; Rocks, Sand, Pottery, Stone Sediments, Volcanic lava, Daub.

So we can tell when a hearth was last lit, a pot was fired in a kiln, a volcano erupted or sand buried. This method can produce dates from as low as 30-50 years, up to almost one million years. The technique that uses heat to find the date is called Thermo luminescence and that which uses light is called Optical Stimulation Luminescence.