Such calibrated dates are expressed as cal BP, where "cal" indicates "calibrated years", or "calendar years", before 1950.Carbon dating uses an unstable isotope of carbon to find the date of dead substances.
(For brevity's sake, hereafter I will refer to the parent isotope as ).
In addition, it requires that these measurements be taken from several different objects which all formed at the same time from a common pool of materials.
This isotope Carbon-14 has a half life of 5,700 years.
The ratio of Carbon-14 remaining indicates the times since the death of a living substance.
Some archaeologists use the lowercase letters bp, bc and ad as terminology for uncalibrated dates for these eras. Beginning in 1954, metrologists established 1950 as the origin year for the BP scale for use with radiocarbon dating, using a 1950-based reference sample of oxalic acid. Currie Lloyd: The problem was tackled by the international radiocarbon community in the late 1950s, in cooperation with the U. Radiocarbon measurements are compared to this modern carbon value, and expressed as "fraction of modern" (f M).