Jump to content

Before Present

From Wikipedia, the free encyclopedia
(Redirected fromBefore present)
"YBP" and "ybp" redirect here. For other uses, seeYBP (disambiguation).

Before Present(BP) or "years before present(YBP) "is atime scaleused mainly inarchaeology,geology, and other scientific disciplines to specify when events occurred relative to the origin of practicalradiocarbon datingin 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 testingartificially altered the proportion of thecarbon isotopesin the atmosphere, which scientists must account for.[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 notationRCYBPstands for the explicit "radio carbon years before present".

Usage

[edit]

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.

Somearchaeologistsuse the lowercase lettersbp,bcandadas terminology for uncalibrated dates for these eras.[10]

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

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

SI prefixes

[edit]

SI prefix multipliersmay 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

[edit]

Radiocarbon datingwas first used in 1949.[14][15]Beginning in 1954,metrologistsestablished 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 aciddihydratewas 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 epochat 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-14tocarbon-12.[18]

Radiocarbon calibration

[edit]
Main article:Radiocarbon dating § Calibration

Dates determined using radiocarbon dating come as two kinds:uncalibrated(also calledLibbyorraw) andcalibrated(also calledCambridge) dates.[19]Uncalibratedradiocarbon 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-14or14C) 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 curvesbased 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

[edit]

Conversion fromGregorian calendaryears 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 thePleistoceneand beginning of theHoloceneepoch[20]
4714 BC 6663 BP Epochof theJulian daysystem: Julian day 0 starts atGreenwichnoon on January 1, 4713 BC of theproleptic Julian calendar,which is November 24, 4714 BC in theproleptic Gregorian calendar[21]: 10 
2251 BC 4200 BP Beginning of theMeghalayanage, the current and latest of the three stages in theHoloceneera.[22][23]
45 BC 1994 BP Introduction of theJulian calendar
1 BC 1950 BP Year zeroinISO 8601
AD 1 1949 BP Beginning of theCommon EraandAnno Domini,from the estimate byDionysiusof theIncarnation of Jesus
1582 368 BP Introduction of theGregorian calendar[21]: 47 
1950 – Epochof the Before Present dating scheme[24]: 190 
2024 74 YAP Current year

See also

[edit]

Citations

[edit]
  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.ISBN978-1-4020-2655-3.Archived fromthe original(PDF)on 2011-07-24.Retrieved8 August2024.
  3. ^abTaylor RE (1985). "The beginnings of radiocarbon dating inAmerican Antiquity:a historical perspective ".American Antiquity.50(2): 309–325.doi:10.2307/280489.JSTOR280489.S2CID163900461.
  4. ^Dincauze, Dena (2000). "Measuring time with isotopes and magnetism".Environmental Archaeology: Principles and Practice.Cambridge, England: Cambridge University Press. p. 110.ISBN978-0-5213-1077-2.
  5. ^"AGU Editorial Style Guide for Authors".American Geophysical Union. 21 September 2007. Archived fromthe originalon 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 originalon 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.S2CID128628228.
  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.S2CID131227900.
  10. ^Edward J. Huth (25 November 1994).Scientific Style and Format: The CBE Manual for Authors, Editors, and Publishers.Cambridge University Press. pp. 495–.ISBN978-0-521-47154-1.Retrieved4 October2012.
  11. ^"The GICC05 time scale".Centre for Ice and Climate – University of Copenhagen. 3 September 2009. Archived fromthe originalon 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.ISSN8755-1209.
  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.JSTOR1677049.PMID15407879.
  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.PMC4853109.PMID27366605.Archived fromthe original(PDF)on 2010-12-06.Retrieved30 October2019. "The Remarkable Metrological History of Radiocarbon Dating [II]"Archived2023-01-01 at theWayback MachineatGoogle 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.PMID17818054.
  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.ISBN0-8122-1828-0.
  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.ISBN978-0-521-70238-6.
  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.PMC4853109.PMID27366605.Archived fromthe original(PDF)on 2010-12-06.Retrieved2018-06-24.

Sources

[edit]
Retrieved from "https://en.wikipedia.org/w/index.php?title=Before_Present&oldid=1241525003"