A method of determining the age of an object by the proportion of ¹⁴C radioactive carbon in the object relative to stable carbon. The method is only applicable to carbon-based material derived from organic matter. In the atmosphere, there is a constant ratio of ¹⁴C to stable carbon, so plants or animals have the same ratio of carbon in their tissues. When an organism dies, it stops taking up carbon from its environment and the proportion of ¹⁴C carbon starts to decrease due to radioactive decay. Since we know the half-life of ¹⁴C carbon (5,730 years), we can easily calculate the time at which the organism died. In the case of archaeology, for example, to determine when a beam was hewn or a piece of cloth woven.