Antiquities can be dated by measuring their natural radioactivity. Popular techniques include "carbon-14 dating" and "thermoluminescence dating". They are useful tools in geological, anthropological and archaeological researches.
Carbon-14 is produced when cosmic rays bombard the atmosphere. The carbon-14 formed will be oxidized to carbon dioxide and absorbed by plants. Meanwhile, animals will ingest plants and hence most of the organic materials contain a certain amount of carbon-14. As soon as the plants or animals die, the uptake of carbon-14 will cease and the amount of carbon-14 will decrease with time due to radioactive decay. The half-life of carbon-14 is about 5,730 years. By measuring the amount of carbon-14 in the ancient organic materials, we can estimate the time when the organism died.
Trace amounts of natural radioactive materials, such as uranium, thorium and potassium with half-lives of up to one billion years, exist in soil. When the inorganic crystal in clay is irradiated by the above radioactive materials, part of the radiation will be released in the form of light and the rest will be trapped in the crystal. When such crystal is heated, the stored energy will be released as light, the so called thermoluminescence effect. Thermoluminescence dating can be used to determine how much time has elapsed since the last time the object was heated. The older the object, the more light will be released. Thermoluminescence dating is commonly used to determine the age of pottery.