Before Present
Before Present (BP, Eng. Ago for today ) in years denotes a time scale that is used in geography, geology, climate science and other sciences to date past events. BP is used for data that were obtained with the radiocarbon dating. It is uncalibrated data, so that can not be directly converted into calendar years.
Because the time is always changed today, January 1, 1950 or the calendar year 1950 was chosen as the reference time scale in the international agreement. The choice of the year 1950 is explained by the practical utilization of the radiocarbon dating in the 1950s. Also, the natural ratio of carbon isotopes in the atmosphere was changed after this reference time by nuclear weapons testing artificial.
After the turn of the millennium a dissatisfaction with the reference year 1950 and the consequent crooked conversion factors emerged. Therefore, since increasingly no longer bp with reference year 1950, but used b2k: before 2000, before 2000.
- 2.1 DIN ISO 8601
- 2.2 BP in dendrochronology
- 2.3 BP in the Warvenchronologie
Defined use
The radiocarbon dating used for age determination results first raw data that need to be corrected for the specification of the calendar year in two respects.
Scattering
Firstly, there is the statistical inaccuracy of the method, which is always subject to variation. It depends on the age of the specimen and is delivered as a scattering width.
However, this Rohzeitangabe needs for the purpose of comparability esp. with historical events of the calibration.
Calibration
Radiocarbon dating is based on the relationship between different isotopes of carbon. In the atmosphere created constantly exposed to sunlight from the normal form of carbon with a mass number of 12 isotopes with mass numbers of 13 and 14, all three isotopes are incorporated in their natural ratio by the metabolism in all living organisms. With the death of the organism ends of metabolism and no new carbon atoms longer built into the organism. The slightly radioactive isotope 14C decays with a characteristic half-life, so that his share towards the stable normal form of 12C over time decreases since the death of the organism.
Because the rate of 14C production in the atmosphere and thus the ratio of the isotopes in the course of thousands of years is not constant and also in nuclear weapons tests was changed artificially by the people, the calculation of the decay time is not the true calendar years. Instead, the results obtained by other methods on the basis of a curve of the relationship between the isotope over time to be corrected. This correction is called calibration. The methods for obtaining the curves are used in particular dendrochronology, ice core studies and for long geological periods, the inclusion of carbon in inorganic materials, especially rocks.
The curves used for calibration be performed by several institutes and constantly improved. They are contained in different software programs. This calibration software, such as OxCal or CalPal can therefore both among themselves as well as between the different versions provide different calibrated time information. Therefore, the calibration software and calibration method should be called at the time indication. Ultimately, these programs provide then a comparable calendrical time specification:
Or
Times
DIN ISO 8601
Date and time information is provided according to the internationally binding DIN ISO 8,601th Alternatively, in ( Western Christian ) press products and publications will now invalid number "v. BC "and" AD AD "(English BCE or CE ) handed down to distinguish annual data before and after the commencement of the Christian era, for example, according to DIN 1355 of 1975. Moreover there is rarely even the spelling "v. CE "or similar.
Very rarely found in geophysical work nor the abbreviation " AP", English for "after present" (equivalent to " 1950 ").
The time specification ago today is especially recommended for those areas in which 1950 or 2000 years interdisciplinary play no role, such as geological information beyond 100,000 years ago.
The sporadically encountered using bp for uncalibrated and calibrated BP for 14C - time data does not correspond to the general modern practice and is rarely used today.
BP in dendrochronology
In archeology and the prehistory and early history and dendrochronology calibrated calendar, which currently goes back to central Europe to -10 461, use dates after DIN ISO 8,601th date and time values, which are in the history older than the early Euro- Mediterranean Neolithic be specified on the time scale in years Before Present.
BP in the Warvenchronologie
The undefined use of the term BP is also in the Warvenchronologie to confusion if they - what is usually necessary due to the incompleteness of the archives - was calibrated by means of one or more 14C - dated reference points. For a proper understanding of the chronology, it is therefore very important to document the extensive additions necessary for the used BP data, namely both with uncalibrated scattering and laboratory abbreviations, and calibrated with an indication of the program used, as these differ in no small measure.