Worldlex Wiki In a convention that is not always observed, many sources restrict the use of BP dates to those produced with radiocarbon dating; the alternative notation "RCYBP" stands for the explicit "radio carbon years before present".
stratigraphy. This usage differs from the recommendation by van der Plicht & Hogg, followed by the Quaternary Science Reviews, both of which recommended that publications use the unit "a" (for "annum", Latin for "year") and reserve the term "BP" for radiocarbon estimations.Some archaeologists use the lowercase letters bp, bc and ad as terminology for uncalibrated dates for these eras.
The Centre for Ice and Climate at the University of Copenhagen instead uses the unambiguous "b2k", for "years before 2000 AD", often in combination with the GreenlandIce Core Chronology 2005 (GICC05) time scale.
Some authors who use the YBP dating format also use "YAP" ("years after present") to denote years after 1950.
SI prefixes
SI prefix multipliers may be used to express larger periods of time, e.g., ka BP (thousand years BP), Ma BP (million years BP) and many others.
Radiocarbon dating
The problem was tackled by the international radiocarbon community in the late 1950s, in cooperation with the U.S. National Bureau of Standards. A large quantity of contemporary oxalic aciddihydrate was prepared as NBS Standard Reference Material (SRM) 4990B. Its 14C concentration was about 5% above what was believed to be the natural level, so the standard for radiocarbon dating was defined as 0.95 times the 14C concentration of this material, adjusted to a 13C reference value of −19 per mil (PDB). This value is defined as "modern carbon" referenced to AD 1950. Radiocarbon measurements are compared to this modern carbon value, and expressed as "fraction of modern" (fM). "Radiocarbon ages" are calculated from fM using the exponential decay relation and the "Libby half-life" 5568 a. The ages are expressed in years before present (BP) where "present" is defined as AD 1950.
The year 1950 was chosen because it was the standard astronomical epoch at that time.atmospheric testing of nuclear weapons, which altered the global ratio of carbon-14 to carbon-12.
Radiocarbon calibration
Many scholarly and scientific journals require that published calibrated results be accompanied by the name (standard codes are used) of the laboratory concerned, and other information such as confidence levels, because of differences between the methods used by different laboratories and changes in calibrating methods.
Conversion
Conversion from Gregorian calendar years to Before Present years is by starting with the 1950-01-01 epoch of the Gregorian calendar and increasing the BP year count with each year into the past from that Gregorian date.
For example, 1000 BP corresponds to 950 AD, 1949 BP corresponds to 1 AD, 1950 BP corresponds to 1 BC, 2000 BP corresponds to 51 BC.
| 9701 BC | Pleistocene and beginning of the Holocene epoch | |
|---|---|---|
| 4714 BC | 6663 BP | Epoch of the Julian day system: Julian day 0 starts at Greenwich noon on January 1, 4713 BC of the proleptic Julian calendar, which is November 24, 4714 BC in the proleptic Gregorian calendar |
| 2251 BC | 4200 BP | Beginning of the Meghalayan age, the current and latest of the three stages in the Holocene era. |
| 45 BC | 1994 BP | Introduction of the Julian calendar |
| 1 BC | 1950 BP | Year zero in ISO 8601 |
| AD 1 | 1949 BP | Beginning of the Common Era and Anno Domini, from the estimate by Dionysius of the Incarnation of Jesus |
| 1582 | 368 BP | Introduction of the Gregorian calendar |
| 1950 | 0000 AP | Epoch of the Before Present dating scheme |
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