Effective range of carbon dating
Nowadays, the internationally agreed upon calendar calibration curves reach as far back as about 48000 BC (Reimer et.
This tree-ring sequence, established by Wesley Ferguson in the 1960s, aided Hans Suess to publish the first useful calibration curve.
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).
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.