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Before Present

From Wikipedia, the free encyclopedia
(Redirected fromYBP)
Time scale used in scientific disciplines
"YBP" and "ybp" redirect here. For other uses, seeYBP (disambiguation).

Before Present (BP) or "years before present (YBP)" is atime scale used mainly inarchaeology, geology, and other scientific disciplines to specify when events occurred relative to the origin of practicalradiocarbon 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, with 1950 being labelled as the "standard year". The abbreviation "BP" has been interpreted retrospectively as "Before Physics",[1][2] which refers to the time beforenuclear weapons testing artificially altered the proportion of thecarbon isotopes in the atmosphere, which scientists must account for when using radiocarbon dating for dates of origin that may fall after this year.[3][4]

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

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The BP scale is sometimes used for dates established by means other than radiocarbon dating, such asstratigraphy.[5][6] This usage differs from the recommendation by van der Plicht & Hogg,[7] followed by theQuaternary Science Reviews,[8][9] both of which requested that publications should use theunit "a" (for "annum", Latin for "year") and reserve the term "BP" for radiocarbon estimations.

Somearchaeologists use the lowercase lettersbp,bc andad as terminology for uncalibrated dates for these eras.[10]

The Centre for Ice and Climate at theUniversity of Copenhagen instead uses the unambiguous "b2k", for "years before 2000 AD", often in combination with theGreenlandIce Core Chronology 2005 (GICC05) time scale.[11]

Some authors who use the YBP dating format also use "YAP" ("years after present") to denote years after 1950.[12]

SI prefixes

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SI prefix multipliers may be used to express larger periods of time, e.g.ka BP (thousand years BP),Ma BP (million years BP) andmany others.[13]

Radiocarbon dating

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Radiocarbon dating was first used in 1949.[14][15] 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 ofoxalic 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.National Bureau of Standards. A large quantity of contemporaryoxalic aciddihydrate was prepared as NBS Standard Reference Material (SRM) 4990B. Its14C 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 the14C concentration of this material, adjusted to a13C 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.[16]

The year 1950 was chosen because it was the standardastronomical epoch at that time.[citation needed] It also marked[3] the publication of the first radiocarbon dates in December 1949,[17] and 1950 also antedates large-scaleatmospheric testing of nuclear weapons, which altered the global ratio ofcarbon-14 tocarbon-12.[18]

Radiocarbon calibration

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Main article:Radiocarbon dating § Calibration

Dates determined using radiocarbon dating come as two kinds:uncalibrated (also calledLibby orraw) andcalibrated (also calledCambridge) dates.[19]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 or14C) has not been strictly constant during the span of time that can be radiocarbon-dated. Uncalibrated radiocarbon ages can be converted to calendar dates bycalibration curves based on comparison of raw radiocarbon dates of samples independently dated by other methods, such asdendrochronology (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

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Conversion fromGregorian 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 yearBP yearEvent
9701 BC11650 BPEnd of thePleistocene and beginning of theHolocene epoch[20]
4714 BC6663 BPEpoch of theJulian day system: Julian day 0 starts atGreenwich noon on January 1, 4713 BC of theproleptic Julian calendar, which is November 24, 4714 BC in theproleptic Gregorian calendar[21]: 10 
2251 BC4200 BPBeginning of theMeghalayan age, the current and latest of the three stages in theHolocene era.[22][23]
45 BC1994 BPIntroduction of theJulian calendar
1 BC1950 BPYear zero inISO 8601
AD 11949 BPBeginning of theCommon Era andAnno Domini, from the estimate byDionysius of theIncarnation of Jesus
1582368 BPIntroduction of theGregorian calendar[21]: 47 
19500000 APEpoch of the Before Present dating scheme[24]: 190 
20250075 APCurrent year

See also

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Citations

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  1. ^Flint, Richard Foster; Deevey, Edward S (1962)."Volume 4 – 1962".Radiocarbon.4 (1): i.
  2. ^van der Plicht, Johannes (January 2004). "Radiocarbon, the Calibration Curve and Scythian Chronology".NATO Science Series: IV: Earth and Environmental Sciences(PDF). Vol. 42. Dordrecht: Springer Netherlands. pp. 45–61 (47).doi:10.1007/1-4020-2656-0_5.ISBN 978-1-4020-2655-3. Archived fromthe original(PDF) on 2011-07-24. Retrieved8 August 2024.
  3. ^abTaylor RE (1985). "The beginnings of radiocarbon dating inAmerican Antiquity: a historical perspective".American Antiquity.50 (2):309–325.doi:10.2307/280489.JSTOR 280489.S2CID 163900461.
  4. ^Dincauze, Dena (2000). "Measuring time with isotopes and magnetism".Environmental Archaeology: Principles and Practice. Cambridge, England: Cambridge University Press. p. 110.ISBN 978-0-5213-1077-2.
  5. ^"AGU Editorial Style Guide for Authors". American Geophysical Union. 21 September 2007. Archived fromthe original on 2008-07-14. Retrieved2009-01-09.
  6. ^North American Commission on Stratigraphic Nomenclature (November 2005)."North American Stratigraphic Code: Article 13 (c)".The American Association of Petroleum Geologists Bulletin.89 (11):1547–1591.doi:10.1306/07050504129. Archived fromthe original on 2014-02-02. Retrieved2009-06-29.
  7. ^van der Plicht, Johannes; Hogg, Alan (2006)."A note on reporting radiocarbon"(PDF).Quaternary Geochronology.1 (4):237–240.Bibcode:2006QuGeo...1..237V.doi:10.1016/j.quageo.2006.07.001.S2CID 128628228.
  8. ^"The use of time units in Quaternary Science Reviews".Quaternary Science Reviews.26 (9–10): 1193. May 2007.Bibcode:2007QSRv...26.1193..doi:10.1016/j.quascirev.2007.04.002.
  9. ^Wolff, Eric W. (December 2007). "When is the "present"?".Quaternary Science Reviews.26 (25–28):3023–3024.Bibcode:2007QSRv...26.3023W.doi:10.1016/j.quascirev.2007.10.008.S2CID 131227900.
  10. ^Edward J. Huth (25 November 1994).Scientific Style and Format: The CBE Manual for Authors, Editors, and Publishers. Cambridge University Press. pp. 495–.ISBN 978-0-521-47154-1. Retrieved4 October 2012.
  11. ^"The GICC05 time scale". Centre for Ice and Climate – University of Copenhagen. 3 September 2009. Archived fromthe original on 18 September 2018. RetrievedSeptember 17, 2018.
  12. ^Berger, André (1988)."Milankovitch Theory and Climate".Reviews of Geophysics.26 (4):624–657.Bibcode:1988RvGeo..26..624B.doi:10.1029/RG026i004p00624.ISSN 8755-1209.
  13. ^Martin Kölling (2015)."Numerous ways to say "thousand years" in a scientific paper". Universität Bremen: Marine Geochemistry - Laboratory Methods. Retrieved2023-03-24.
  14. ^Arnold, J.R.; Libby, W.F. (1949)."Age determinations by radiocarbon content: checks with samples of known age".Science.110 (2869):678–680.Bibcode:1949Sci...110..678A.doi:10.1126/science.110.2869.678.JSTOR 1677049.PMID 15407879.
  15. ^Aitken (1990), pp. 60–61.
  16. ^Currie, Lloyd A (March–April 2004)."The Remarkable Metrological History of Radiocarbon Dating [II]"(PDF).Journal of Research of the National Institute of Standards and Technology.109 (2):185–217.doi:10.6028/jres.109.013.PMC 4853109.PMID 27366605. Archived fromthe original(PDF) on 2010-12-06. Retrieved30 October 2019."The Remarkable Metrological History of Radiocarbon Dating [II]"Archived 2023-01-01 at theWayback Machine atGoogle Books (accessed 30 October 2019).
  17. ^Arnold JR, Libby WF (1949-03-04). "Age determinations by radiocarbon content: Checks with samples of known age".Science.109 (2827):227–228.Bibcode:1949Sci...109..227L.doi:10.1126/science.109.2827.227.PMID 17818054.
  18. ^"Nuclear Bombs Made It Possible to Carbon Date Human Tissue".Smithsonian Magazine. 2013-02-19. Retrieved2020-01-09.
  19. ^Greene, Kevin (2002).Archaeology: An Introduction. Philadelphia: University of Pennsylvania Press. pp. 165–167.ISBN 0-8122-1828-0.
  20. ^Walker, Mike; Jonsen, Sigfus; Rasmussen, Sune Olander; Popp, Trevor; Steffensen, Jørgen-Peder; Gibbard, Phil; Hoek, Wim; Lowe, John; Andrews, John;Björck, Svante; Cwynar, Les C.; Hughen, Konrad; Kershaw, Peter; Kromer, Bernd; Litt, Thomas; Lowe, David J.; Nakagawa, Takeshi; Newnham, Rewi; Schwander, Jacob (2009)."Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records"(PDF).Journal of Quaternary Science.24 (1):3–17.Bibcode:2009JQS....24....3W.doi:10.1002/jqs.1227.Archived(PDF) from the original on 2013-11-04.
  21. ^abDershowitz, Nachum;Reingold, Edward M. (2008).Calendrical Calculations (3rd ed.). Cambridge University Press.ISBN 978-0-521-70238-6.
  22. ^"ICS chart containing the Quaternary and Cambrian GSSPs and new stages (v 2018/07) is now released!". RetrievedFebruary 6, 2019.
  23. ^Conners, Deanna (September 18, 2018)."Welcome to the Meghalayan age". RetrievedFebruary 6, 2019.
  24. ^Currie Lloyd A (2004)."The Remarkable Metrological History of Radiocarbon Dating [II]"(PDF).Journal of Research of the National Institute of Standards and Technology.109 (2):185–217.doi:10.6028/jres.109.013.PMC 4853109.PMID 27366605. Archived fromthe original(PDF) on 2010-12-06. Retrieved2018-06-24.

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