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And indeed, results of calibration are often given as an age range rather than an absolute value.
Age ranges are calculated either by the intercept method or the probability method, both of which need a calibration curve.
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.
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.
It is also called “radiocarbon” because it is unstable and radioactive relative to carbon-12 and carbon-13.
Carbon consists of 99% carbon-12, 1% carbon-13, and about one part per million carbon-14.
At present, tree rings are still used to calibrate radiocarbon determinations.
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.
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.