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Beginning in 1954, metrologists established 1950 as the origin year for the BP scale for use with , which altered the global ratio of Carbon-14 to Carbon-12 . AD or BC? from www.ScienceCourseware.org The BP scale is now in common use for dates established by means other than radiocarbon dating. The practice of anchoring "the present" at 1950 is generally followed, although times in the distant past (e.g., 500,000 BP) typically have uncertainties high enough that the difference between 1950 and the actual present year is insignificant. RADIOCARBON DATING AND CALIBRATION Dates determined using radiocarbon dating come in two kinds: ''uncalibrated'' (or "raw") and ''calibrated''. Uncalibrated radiocarbon dates may be expressed using BP years; however, they are not identical to calendar dates. This has to do with the fact that the level of atmospheric radiocarbon ( Carbon-14 or 14C) has not been strictly constant during the span of time that can be radiocarbon-dated. Uncalibrated radiocarbon ages can be converted to calendar dates by means of Calibration Curves based on comparison of raw radiocarbon dates of samples independently dated by other methods, such as Dendrochronology (the examination of tree growth-rings). Such calibrated dates are expressed as cal BP, where "cal" indicates "calendar years" or "calibrated years". SEE ALSO REFERENCES |
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