Radiocarbon Dating

One of the most important questions asked about any ancient object is just how old it really is. There are a number of scientific techniques which can be used to date antiquities, but probably the best known and most frequently used is radiocarbon or 14C dating. Radiocarbon dating can only be applied to organisms that were once alive and is a means of determining how long ago they died.

Radiocarbon dating is possible because of the existence in nature of a tiny amount of 14C, or radiocarbon, a radioactive isotope of carbon. This isotope is produced in the upper atmosphere by the action of cosmic rays on 14N. This 14C combines with oxygen to produce carbon dioxide (CO2) and is taken in by plants during photosynthesis. From plants this 14C is absorbed into the tissues of every living thing via the food chain. Since it is radioactive, it is unstable and decays away at a known rate. While any plant or animal is alive the 14C lost by radioactive decay is constantly replaced through the food chain, but when that organism dies, no more 14C is taken in, and the amount present in the tissues goes down.

By measuring how much 14C remains in ancient organic materials, it is possible to calculate how long ago they died. To do this requires extensive chemical processing, carried out in laboratories like that of the British Museum To convert the carbon in the ancient objects to a form in which the very low level radioactivity (way below background levels) can be measured. Most radiocarbon dating is carried out on bone or charcoal, as these are the organics that most frequently survive from the past, but many other materials can also be dated using this technique.

Further Reading

S Bowman, Radiocarbon Dating (British Museum Press, 1990)

For details on the science behind Radiocarbon dating visit Radiocarbon-WEB

For more information on radiocarbon laboratories world-wide visit the Radiocarbon home page