Calibration curve for the radiocarbon dating scale
Suess’s curve, based on the bristlecone pine, used tree rings for its calendar axis.There have been many calibration curves published since Suess’s curve, but their proliferation brought more problems than solutions.These changes were brought about by several factors including, but not limited to, fluctuations in the earth’s geomagnetic moment, fossil fuel burning, and nuclear testing.The most popular and often used method for calibration is by dendrochronology.Tree rings provided truly known-age material needed to check the accuracy of the carbon-14 dating method.During the late 1950s, several scientists (notably the Dutchman Hessel de Vries) were able to confirm the discrepancy between radiocarbon ages and calendar ages through results gathered from carbon dating rings of trees.Results of carbon-14 dating are reported in radiocarbon years, and calibration is needed to convert radiocarbon years into calendar years.Uncalibrated radiocarbon measurements are usually reported in years BP where 0 (zero) BP is defined as AD 1950.
In practice, tree-ring calibration is not as straightforward due to many factors, the most significant of which is that individual measurements made on the tree rings and the sample have limited precision so a range of possible calendar years is obtained.
For the period after 1950, a great deal of data on atmospheric radiocarbon concentration is available.
Post-modern data are very useful in some cases in illustrating a calendar age of very young materials (Hua, et. Atmospheric Radiocarbon for the period 1950-2010, Radiocarbon, 55(4), 2013).
Radiocarbon dating laboratories have been known to use data from other species of trees.
In principle, the age of a certain carbonaceous sample can be easily determined by comparing its radiocarbon content to that of a tree ring with a known calendar age.