HOME
TheInfoList



Before Present (BP) years is a time scale used mainly in
archaeology Archaeology or archeology is the study of human activity through the recovery and analysis of material culture. Archaeology is often considered a branch of socio-cultural anthropology, but archaeologists also draw from biological, geological ...
,
geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the processes by which th ...
, and other scientific disciplines to specify when events occurred before the origin of practical
radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive Isotopes of carbon, isotope of carbon. ...
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"; that refers to the time before nuclear weapons testing artificially altered the proportion of the carbon isotopes in the atmosphere, making dating after that time likely to be unreliable. 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 is explicitly Radio Carbon Years Before Present.


Usage

The BP scale is sometimes used for dates established by means other than radiocarbon dating, such as
stratigraphy through Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic period million years ago (Year, Mya) to the beginning of the Cretaceous period ap ...
. This usage differs with the recommendation by van der Plicht & Hogg, followed by the ''Quaternary Science Reviews'', both of which requested that publications should 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 has proposed "b2k" as "years before AD 2000", based on the
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is the world's largest island, located between the Arctic The Arctic ( or ) is a polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocea ...
Ice Core Chronology 2005 (GICC05) time scale.


Radiocarbon dating

Radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive Isotopes of carbon, isotope of carbon. ...
was first used in 1940. 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 of
oxalic acid
oxalic acid
. According to scientist A. Currie Lloyd: The year 1950 was chosen because it was the standard astronomical epoch at that time. It also marked the publication of the first radiocarbon dates in December 1949, and 1950 also antedates large scale nuclear testing, atmospheric testing of nuclear weapons, which altered the global ratio of carbon-14 to carbon-12.


Radiocarbon calibration

Dates determined using radiocarbon dating come as two kinds: ''uncalibrated'' (also called ''Libby'' or ''raw'') and ''calibrated'' (also called ''Cambridge'') dates. ''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 means of Radiocarbon dating#Calibration, calibration curves based on comparison of raw radiocarbon dates of samples independently dated by other methods, such as dendrochronology (dating on the basis of tree growth-rings) and
stratigraphy through Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic period million years ago (Year, Mya) to the beginning of the Cretaceous period ap ...
(dating on the basis of 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/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.


See also

*Anthropocene


Footnotes


Citations

{{Chronology Calendar eras Geochronology