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.Tree rings provided truly known-age material needed to check the accuracy of the carbon-14 dating method.
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.
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.
Radiocarbon measurements are based on the assumption that atmospheric carbon-14 concentration has remained constant as it was in 1950 and that the half-life of carbon-14 is 5568 years.