4.4 Radiocarbon Dating

Radiocarbon (or simply carbon) dating is probably the most famous method in archaeology. Although it is not as powerful as depictions on TV may display, it is still a potent window to access the past.

How it Works

Radiocarbon datingA scientific method that uses the decay of carbon-14 in organic material to determine its age, up to around 50,000 years old., as well as being particularly famous, is particularly complex. The method rests on the ability to measure different isotopes of carbon relative to one another. A deeper description of the use of elemental isotopes in archaeology is available in the next module, but this method does not need to have as much detail to be understood effectively.

Carbon-14 (\(\ce{^{14}C}\)) is one of the isotopes of carbon present in the world, often simply called radiocarbon. Radiocarbon is constantly produced in the atmosphere as a result of cosmic and solar rays interacting with nitrogen-14 and producing \(\ce{^{14}C}\). Due to its radioactivity, \(\ce{^{14}C}\) has a half-lifeThe time it takes for half the atoms of a radioactive substance to decay; for carbon-14, this is approximately 5,700 years. - a period of time after which half a sample of \(\ce{^{14}C}\) has decayed. For \(\ce{^{14}C}\), the half-life is ~5,700±30 years. Carbon-12 and carbon-13 are stable isotopes of carbon, meaning they are not radioactive and thus have no half-life and experience no decay. 

Carbon is fundamental to most biological processes, and as a result \(\ce{^{12}C}\), \(\ce{^{13}C}\), and \(\ce{^{14}C}\) are all incorporated into biological material. This incorporation ceases after the death of the plant or animal, meaning a set reservoir of different carbon isotopes are present in any dead biological material. As such, any biological material will contain varying amounts of \(\ce{^{12}C}\), \(\ce{^{13}C}\), and \(\ce{^{14}C}\) dependent both on their abundance in the natural world and the decay that the \(\ce{^{14}C}\) has undergone.

By measuring the ratio between radiocarbon and stable carbon isotopes, we can calculate the amount of half-lives (or what portion of a half-life) the \(\ce{^{14}C}\) has undergone in comparison to the expected ratio of radiocarbon to stable carbon. To do this properly, however, the results need to undergo calibration.