Calibration Curves 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.

When was tree-ring invented?

1920s The method was invented in the 1920s by astronomer Andrew Ellicott Douglass and archaeologist Clark Wissler.