Radiocarbon dating after 1950
Radiocarbon measurements are always reported in terms of years `before present' (BP).
The first indicates the proportion of radiocarbon atoms in the sample as compared to samples modern in 1950.
The second is directly derived from this on the assumption that the half-life of radiocarbon is 5568 years and the amount of radiocarbon in the atmosphere has been constant.
For older periods we are able to use other records of with idependent age control to tell us about how radiocarbon changed in the past.
The information from measurements on tree rings and other samples of known age (including speleothems, marine corals and samples from sedimentary records with independent dating) are all compiled into calibration curves by the Int Cal group.
Once calibrated a radiocarbon date should be expressed in terms of cal BC, cal AD or cal BP.
The cal prefix indicates that the dates are the result of radiocarbon calibration using tree ring data.
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.
This plot shows how the radiocarbon measurement 3000 -30BP would be calibrated.
The left-hand axis shows radiocarbon concentration expressed in years `before present' and the bottom axis shows calendar years (derived from the tree ring data).
See also ORAU's Explanation of Radiocarbon Results.Tags: Adult Dating, affair dating, sex dating