Years before present. The ‘present’ referred to is the year ad 1950, the latest that the atmosphere was sufficiently uncontaminated to act as a standard for radiocarbon dating. The lower case ‘bp’-represents uncalibrated radiocarbon years; the capitals bp denote a calibrated radiocarbon date,or a date derived from some other dating method, such as potassium-argon, that does not need calibration (see Table 8, page 422).
The Macmillan dictionary of archaeology, Ruth D. Whitehouse, 1983Copied