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.
At present, tree rings are still used to calibrate radiocarbon determinations.
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.
Calibration of radiocarbon results is needed to account for changes in the atmospheric concentration of carbon-14 over time.
They can determine the exact calendar year each tree ring was formed.
Dendrochronological findings played an important role in the early days of radiocarbon dating.