Radiocarbon dating to
See also ORAU's Explanation of Radiocarbon Results.Radiocarbon dates should always be reported either as `percent modern' or years `before present' (BP).There are two main methods used for calculating age ranges from the calibration curve: The first method to be employed was called the `intercept method' because it can be done by drawing intercepts on a graph.This method will tell you the years in which the radiocarbon concentration of tree rings is within two standard deviations of your measurement (e.g.The wood in these rings once laid down remains unchanged during the life of the tree.This is very useful as a record of the radiocarbon concentration in the past.By using dead trees of different but overlapping ages, you can build up a library of tree rings of different calendar ages.This has now been done for Bristlecone Pines in the U. A and waterlogged Oaks in Ireland and Germany, and Kauri in New Zealand to provide records extending back over the last 14,000 years.
The grey histogram shows possible ages for the sample (the higher the histogram the more likely that age is).
It is calculated on the assumption that the atmospheric radiocarbon concentration has always been the same as it was in 1950 and that the half-life of radiocarbon is 5568 years.
For this purpose `present' refers to 1950 so you do not have to know the year in which the measurement was made.
These are the basis for the calibrations performed by the programs like CALIB and Ox Cal. Calibration of radiocarbon determinations is in principle very simple.
If you have a radiocarbon measurement on a sample, you can try to find a tree ring with the same proportion of radiocarbon.