ABSTRACT

Carbon-14 dating (Taylor, 1997) is regularly applied to the organic component of bone called collagen, including bones from caves, with varying degrees of success. Radiogenic 14C is produced in the upper atmosphere by cosmic rays at a more-or-less constant rate. Living organisms take up 14C as well as the stable isotopes, 13C and 12C. After death, there is no 14C replenishment and the 14C decays by beta particle emission at a rate determined by its half-life of 5568±30 years. As the rate of production of

radiogenic 14C is not quite constant over time, a correction has to be made using a treering master curve. The resulting date is quoted as radiocarbon calibrated (“cal” for short; e.g. 7680±150 BP cal, where BP stands for “Before Present”, and where “present” is 1950). The normal limit of the dating method without calibration is about 40-50000 years, depending on the sample and upon the laboratory set-up. Many samples are now dated using an accelerator mass spectrometer (AMS) that measures the ratio of 14C to 12C isotopes rather than the number of beta decays. Beyond the range of tree-ring calibration, 14C dates have been cross-calibrated using Uranium-Thorium (U-Th) dates and these indicate that a radiocarbon age of 18000 years is too low by 2000 years and a radiocarbon age of 36000 years may be too low by about 4000 years, though this latter remains to be confirmed.