Bonekickers

History behind ‘Army of God’: Carbon-14 Dating

Carbon-14 dating is the commonest way to scientifically date organic material. The technique is based on the principle of radioactive decay of the ¹⁴C isotope that has a half-life of 5,730 years.

The proportion of ¹⁴C in the atmosphere is relatively stable, being formed by cosmic ray radiation. When this is incorporated into living organisms, the radiocarbon clock is effectively started, so the older the sample the lower the proportion of ¹⁴C. The limit of this technique is around 50,000 years, and it cannot be used to date samples after about 1700 AD, due to the large quantities of fossil carbon released into the atmosphere, and most recently the effect of nuclear testing.

A calendar date requires calibration from the radiocarbon age (expressed as years before present or BP, with a stated error margin). Calibration calculations give different levels of probability for particular dates: multiple dates from secure archaeological contexts can be combined using statistical methods to give even greater accuracy.