Compare and contrast radiometric dating with tree rings.

Uncalibrated radiocarbon measurements are usually reported in years BP where 0 (zero) BP is defined as AD 1950. BP stands for "Before Present" or "Before Physics" as some would refer to it. It should be noted that a BP notation is also used in other dating techniques but is defined differently, as in the case of thermoluminescence dating wherein BP is defined as AD 1980.