Before Present

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".

^ Flint, Richard Foster; Deevey, Edward S (1962). "Volume 4 – 1962". Radiocarbon. 4 (1): i.
^ Taylor RE (1985). "The beginnings of radiocarbon dating in American Antiquity: a historical perspective". American Antiquity. 50 (2): 309–325. doi:10.2307/280489. JSTOR 280489. S2CID 163900461.
^ 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.

[1] Flint, Richard Foster; Deevey, Edward S (1962). "Volume 4 – 1962". Radiocarbon. 4 (1): i.

[Taylor-2] Taylor RE (1985). "The beginnings of radiocarbon dating in American Antiquity: a historical perspective". American Antiquity. 50 (2): 309–325. doi:10.2307/280489. JSTOR 280489. S2CID 163900461.

[3] 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.

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