Effective range of carbon dating
The first calibration curve for radiocarbon dating was based on a continuous tree-ring sequence stretching back to 8,000 years.This tree-ring sequence, established by Wesley Ferguson in the 1960s, aided Hans Suess to publish the first useful calibration curve.
Calibration of radiocarbon results is needed to account for changes in the atmospheric concentration of carbon-14 over time.In later years, the use of accelerator mass spectrometers and the introduction of high-precision carbon dating have also generated calibration curves.A high-precision radiocarbon calibration curve published by a laboratory in Belfast, Northern Ireland, used dendrochronology data based on the Irish oak.Calibration is not only done before an analysis but also on analytical results as in the case of radiocarbon dating—an analytical method that identifies the age of a material that once formed part of the biosphere by determining its carbon-14 content and tracing its age by its radioactive decay.Carbon-14 is a naturally occurring isotope of the element carbon.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).
The tree rings were dated through dendrochronology.
At present, tree rings are still used to calibrate radiocarbon determinations.
If a sample has the same proportion of radiocarbon as that of the tree ring, it is safe to conclude that they are of the same age.
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.
Tree rings provided truly known-age material needed to check the accuracy of the carbon-14 dating method.