Dates determined using radiocarbon dating come as two kinds: uncalibrated (also called Libby or raw) and calibrated (also called Cambridge) dates. Such calibrated dates are expressed as cal BP, where cal indicates calibrated years, or calendar years, before 1950.

## What is the difference between radiocarbon years and calibrated radiocarbon years?

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.

## Is BP the same as BC?

Dates can be expressed as AD, BC, BCE (before common era), and BP (before present). The accepted way to represent C-14 ages is in terms of years BP, where the year 1950 is used as the present. (1950 is the date that the calibration curves were established.