Before Present

Source: Wikipedia, the free encyclopedia.
"YBP" and "ybp" redirect here. For other uses, see YBP (disambiguation).

Before Present (BP) years, also known as "time before present" or "years before present (YBP)", is a time scale used mainly in archaeology, geology, and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Because the "present" time changes, standard practice is to use 1 January 1950 as the commencement date (epoch) of the age scale. The abbreviation "BP" has been interpreted retrospectively as "Before Physics",[1] which refers to the time before nuclear weapons testing artificially altered the proportion of the carbon isotopes in the atmosphere, which scientists must account for.[2][3]

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".

Usage

The BP scale is sometimes used for dates established by means other than radiocarbon dating, such as

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.[9]

The Centre for Ice and Climate at the

Ice Core Chronology 2005 (GICC05) time scale.[10]

Some authors who use the YBP dating format also use YAP (years after present) to denote years after 1950.[11]

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.[12]

Radiocarbon dating

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
. According to scientist A. Currie Lloyd:

The problem was tackled by the international radiocarbon community in the late 1950s, in cooperation with the U.S.

dihydrate 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.[15]

The year 1950 was chosen because it was the standard

atmospheric testing of nuclear weapons, which altered the global ratio of carbon-14 to carbon-12.[17]

Radiocarbon calibration

Main article: Radiocarbon dating § Calibration

Dates determined using radiocarbon dating come as two kinds: uncalibrated (also called Libby or raw) and calibrated (also called Cambridge) dates.[18] Uncalibrated radiocarbon dates should be clearly noted as such by "uncalibrated years BP", because 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 calibration curves based on comparison of raw radiocarbon dates of samples independently dated by other methods, such as dendrochronology (dating based on tree growth-rings) and stratigraphy (dating based on sediment layers in mud or sedimentary rock). Such calibrated dates are expressed as cal BP, where "cal" indicates "calibrated years", or "calendar years", before 1950.

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.

Example milestone years in the BP time scale
Gregorian year BP year Event
9701 BC 11650 BP End of the Pleistocene and beginning of the Holocene epoch[19]
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[20]
: 10 
2251 BC
 4200 BP Beginning of the Meghalayan age, the current and latest of the three stages in the Holocene era.[21][22]
45 BC 1994 BP Introduction of the Julian calendar
1 BC 1950 BP Year zero at 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[20]: 47 
1950 –
Epoch of the Before Present dating scheme[23]
: 190 
2024 74 YAP Current year

See also

Citations

  1. ^ Flint, Richard Foster; Deevey, Edward S (1962). "Volume 4 – 1962". Radiocarbon. 4 (1): i.
  2. ^
    S2CID 163900461
    .
  3. ISBN 978-0-5213-1077-2
    .
  4. ^ "AGU Editorial Style Guide for Authors". American Geophysical Union. 21 September 2007. Archived from the original on 2008-07-14. Retrieved 2009-01-09.
  5. doi:10.1306/07050504129. Archived from the original
    on 2014-02-02. Retrieved 2009-06-29.
  6. ^ van der Plicht, Johannes; Hogg, Alan (2006). "A note on reporting radiocarbon" (PDF).
    S2CID 128628228
    .
  7. ^ "The use of time units in Quaternary Science Reviews". Quaternary Science Reviews. 26 (9–10): 1193. May 2007.
    doi:10.1016/j.quascirev.2007.04.002
    .
  8. S2CID 131227900
    .
  9. ISBN 978-0-521-47154-1
    . Retrieved 4 October 2012.
  10. ^ "The GICC05 time scale". Centre for Ice and Climate – University of Copenhagen. 3 September 2009. Archived from the original on 18 September 2018. Retrieved September 17, 2018.
  11. ISSN 8755-1209
    .
  12. ^ Martin Kölling (2015). "Numerous ways to say "thousand years" in a scientific paper". Universität Bremen: Marine Geochemistry - Laboratory Methods. Retrieved 2023-03-24.
  13. PMID 15407879
    .
  14. ^ Aitken (1990), pp. 60–61.
  15. PMID 27366605. Archived from the original
    (PDF) on 2010-12-06. Retrieved 30 October 2019. "The Remarkable Metrological History of Radiocarbon Dating [II]" Archived 2023-01-01 at the Wayback Machine at Google Books (accessed 30 October 2019).
  16. ^ Arnold JR, Libby WF (1949-03-04). "Age determinations by radiocarbon content: Checks with samples of known age". Science. 109 (2827): 227–228.
    PMID 17818054
    .
  17. ^ "Nuclear Bombs Made It Possible to Carbon Date Human Tissue". Smithsonian Magazine. 2013-02-19. Retrieved 2020-01-09.
  18. ISBN 0-8122-1828-0
    .
  19. ^ Walker, Mike; Jonsen, Sigfus; Rasmussen, Sune Olander; Popp, Trevor; Steffensen, Jørgen-Peder; Gibbard, Phil; Hoek, Wim; Lowe, John; Andrews, John;
    doi:10.1002/jqs.1227. Archived
    (PDF) from the original on 2013-11-04.
  20. ^
    ISBN 978-0-521-70238-6
    .
  21. ^ "ICS chart containing the Quaternary and Cambrian GSSPs and new stages (v 2018/07) is now released!". Retrieved February 6, 2019.
  22. ^ Conners, Deanna (September 18, 2018). "Welcome to the Meghalayan age". Retrieved February 6, 2019.
  23. PMID 27366605. Archived from the original
    (PDF) on 2010-12-06. Retrieved 2018-06-24.

Sources
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