Radiocarbon Dating

Definition: Radiocarbon Dating

Radiocarbon Dating

Noun

1. A chemical analysis used to determine the age of organic materials based on their content of the radioisotope carbon-14; believed to be reliable up to 40,000 years.

Domain	Definitions
Biology & Biotechnology	The determination of the age of old carbon materials by means of the measured content of radiocarbon. Source: European Union. (references)
Geological	The age of organic material determined by the amounts of carbon isotopes 12, 13 and 14. The ratio of 12 to 14 is about the same in all living things but when a plant or animal dies, no more carbon is taken on. Carbon 12 and 13 are stable isotopes and the amounts remain the same even in dead material. Carbon 14 is an radioactive isotope that decays radioactively until none is left; . Thus, the ratio records the time elapsed since death. Since carbon 14 decays relatively rapidly, the method is only reliable for the last 40,000 years. See radiometric age. (references)
Mining	See:carbon-14 dating. (references)
Source: compiled by the editor from various references; see credits.

Radiocarbon dating is the use of a naturally occurring isotope of carbon to determine the age of organic materials.

Carbon has two stable isotopes: carbon-12 (¹²C), and carbon-13 (¹³C). In addition, there are tiny amounts of the unstable (radioactive) isotope carbon-14 (¹⁴C) on earth. ¹⁴C has a half-life of just under 6000 years, and so would have long ago vanished from the earth, were it not for its constant formation by cosmic ray impacts on nitrogen in the earth's atmosphere. When cosmic rays enter the atmosphere they undergo various transformations, including the production of neutrons. The resulting neutrons participate in the following reaction:

n + ¹⁴N → ¹⁴C + ¹H

This reaction is relatively common, as nitrogen constitutes nearly 80% of Earth's atmosphere. The highest rate of carbon-14 production takes place at altitudes of 30,000-50,000 feet, and at higher geomagnetic lattitudes, but the carbon-14 spreads evenly throughout the atmosphere and reacts with oxygen to form carbon dioxide. Carbon dioxide also permeates the oceans, dissolving in the water. Since it is assumed that the cosmic ray flux is constant over long periods of time, carbon-14 is assumed to be continuously produced at a constant rate and therefore that the proportion of radioactive to non-radioactive carbon throughout the Earth's atmosphere and oceans is constant.

Plants take up atmospheric carbon dioxide by photosynthesis, and are eaten by animals, so every living thing is constantly exchanging ¹⁴C with its environment as long as it lives. Once it dies, however, this exchange stops, and the amount of ¹⁴C gradually decreases through radioactive decay. This decay can be used to get a measure of how long ago a piece of once-living material died.

Measurements were originally made by counting the radioactive decay of individual carbon atoms, but this was relatively insensitive and subject to statistical errors: there is never much ¹⁴C to begin with, and a half-life that long means that very few of the atoms will decay while their detection is attempted. Sensitivity and accuracy have since been greatly increased by the use of mass-spectrometric techniques, where the ¹⁴C atoms can be counted directly. Raw radiocarbon measurements are usually reported as years "before present" (BP). This is the number of radiocarbon years before 1950, based on a nominal (and fictitiously constant) level of ¹⁴C in the atmosphere equal to the 1950 level.

Radiocarbon labs generally report an uncertainty, e.g., 3000±30BP indicates a standard deviation of 30 radiocarbon years. Traditionally this includes only the statistical counting uncertainty and some labs supply an "error multiplier" that can be multiplied by the uncertainty to account for other sources of error in the measuring process. Additional error is likely to arise from the nature and collection of the sample itself, e.g., a tree may accumulate carbon over a significant period of time and the wood turned into an artifact some time after the death of the tree. It is sometimes stated that burnt material can be reliably dated to the time of burning.

The maximum range of radiocarbon dating appears to be about 50,000 years, after which the amount of ¹⁴C is too low to be distiguished from background radiation. The K-Ar and uranium decay series are used in dating older objects (see Radiometric dating).

Calibration

The raw BP date can not be used directly as a calendar date, because the assumption that the level of ¹⁴C remains constant does not hold true in practice. The level is maintained by high energy particles interacting with the earth's upper atmosphere, which may be affected by changes in the earth's magnetic field or in the cosmic ray background. In addition there are substantial reservoirs of carbon in organic matter and in the ocean and changing climate can sometimes disrupt the carbon flow between these reservoirs and the atmosphere. The level has also been affected by human activities -- it was almost doubled for a short period due to atomic bomb tests in the 1950s and 1960s and has been reduced by the release of large amounts of CO₂ from ancient organic sources where ¹⁴C is not present -- the fossil fuels used in industry and transportation.

The BP dates are therefore calibrated to give calendar dates. Standard calibration curves are available, based on comparison of radiocarbon dates with other methods such as examination of tree growth rings (dendrochronology), ice and sediment cores and coral samples. The difference between the Julian calendar and the Gregorian calendar can be ignored, because it's insignificant compared to the measurement uncertainty.

The calibration curves can vary significantly from a straight line, so comparison of uncalibrated radiocarbon dates (e.g., plotting them on a graph or subtracting dates to give elapsed time) is likely to give misleading results. There are also significant plateaus in the curves, such as the one at 10000 radiocarbon years BP, which is believed to be associated with changing ocean circulation at the end of the Younger Dryas period. The accuracy of radiocarbon dating is lower for samples originating from such plateau periods.

Libby vs Cambridge half-life

Carbon dating was developed by a team led by Willard Libby. Originally a Carbon-14 half-life of 5568±30 years was used, which is now known as the Libby half-life. Later a more accurate figure of 5730±40 years was measured, which is known as the Cambridge half-life. However laboratories continue to use the Libby figure to avoid confusion. An uncalibrated dating using the Libby figure could be improved by multiplying by the ratio of these numbers (approximately 1.03), but this is usually unnecessary since the adjustment is included in modern calibration curves.

Examples of Carbon Dating and Historical Disputes

Shroud of Turin

Santorini

External links

Synonyms: Radiocarbon Dating

Synonyms: carbon dating (n), carbon-14 dating (n). (additional references)

Crosswords: Radiocarbon Dating

English words defined with "radiocarbon dating": Libby ♦ Willard Frank Libby. (references)

Specialty definitions using "radiocarbon dating": chronometric dating, chronometric method, chronometric technique ♦ dating technique ♦ radiometric age. (references)

Domain	Title
Books	Altersbestimmungen im Quartèar : Datierungen mit Radiokohlenstoff und anderen kernphysikalischen Methoden = Age determination in Quaternary : radiocarbon dating and age estimation with other methods of nuclear physics (reference) Radiocarbon Dating (reference) Radiocarbon Dating New Zealand Prehistory Using Marine Shell (reference) (more book examples)
Source: compiled by the editor from various references; see credits.

The following statistics estimate the number of searches per day across the major English-language search engines as identified by various trade publications. Hyperlinks lead to commercial use of the expression at Amazon.com.

Language		Translations for "radiocarbon dating"; alternative meanings/domain in parentheses.
Danish		kulstof-14 datering, C-14-datering (carbon 14 age, radiocarbon age), C-14-alder (carbon 14 age, radiocarbon age). (various references)

Dutch		radio-koolstofouderdom (carbon 14 age, radiocarbon age), koolstofdatering, C-14-ouderdom (carbon 14 age, radiocarbon age). (various references)

Finnish		iänmääritys radioaktiivisen hiilen avulla (carbon-14 dating). (various references)

French		datation par radiocarbone (radiocarbon age), datation par le carbone 14 (radiocarbon age), datation au carbone 14, détermination au radiocarbone, détermination au carbone 14. (various references)

German		Radiokohlenstoff-Datierung (carbon dating, carbon-14 dating), Radiokarbonmethode, C-14-Datierung (carbon 14 age, carbon-14 dating, radiocarbon age), C-14-Altersbestimmung, C-14 Alter (carbon 14 age, radiocarbon age), 14C-Datierung (carbon dating, carbon-14 dating). (various references)

Greek		χρονολόγηση με ραδιενεργό άνθρακα. (various references)

Italian		et� determinata dal tenore in radiocarbonio (carbon 14 age, radiocarbon age), et� del radiocarbonio (carbon 14 age, radiocarbon age), datazione C-14 (carbon 14 age, radiocarbon age), datazione al radiocarbonio (carbon dating, carbon-14 dating), datazione al carbonio 14. (various references)

Pig Latin		adiocarbonray atingday.(various references)

Portuguese		dataçao por carbono 14 (carbon dating, carbon-14 dating), datação pelo carbono radioactivo. (various references)

Spanish		determinación de la edad por carbono radiactivo, datación radiocarbónica (carbon dating, carbon-14 dating), datación por 14C (carbon dating, carbon-14 dating). (various references)

Swedish		kol-fjorton-datering (carbon 14 age, radiocarbon age), kol-fjorton-ålder (carbon 14 age, radiocarbon age), kol-14-datering (carbon 14 age, carbon-14 dating, radiocarbon age), kol-14-ålder (carbon 14 age, radiocarbon age). (various references)
Source: compiled by the editor from various translation references.

Scrabble® Enable2K-Verified Anagrams
	Words within the letters "a-a-a-b-c-d-d-g-i-i-n-n-o-o-r-r-t"
	-5 letters: barricadoing, carbonadoing, coordinating, nonadiabatic.
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