Radiocarbon dating methodology

Animals (and humans) get their carbon atoms primarily from what they eat (i.e., plants).Thus the ratio of radiocarbon to stable carbon in living animal tissue is also virtually the same as the ratio of radiocarbon to stable carbon in the atmosphere at any given time.The atmosphere contains many stable carbon atoms and relatively few radiocarbon atoms.

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By cross-matching tree-ring sequences in individual specimens a long, continuous tree-ring chronology is constructed with very little dating uncertainty. for more information on tree-ring chronologies.) By measuring radiocarbon concentrations in these tree-rings of known age a calibration table is constructed giving the true date of a sample versus its raw radiocarbon date.

The raw radiocarbon date of any sample can then be converted to true date by using this calibration table.

This ratio is the same for all organisms across the globe at a given time due to the mixing of the atmosphere mentioned above.

When an organism dies (whether plant or animal) its intake of carbon atoms ceases.

This is because the amount and strength of cosmic radiation entering the earth's atmosphere has varied over time.

(This, in turn, is caused by variations in the magnetic fields of the earth and sun, for example.) Although the ratio of radiocarbon to stable carbon in the atmosphere has varied over time, it is quite uniform around the globe at any given time because the atmosphere mixes very quickly and constantly.

Both radiocarbon and optically stimulated luminescence (OSL) dating methods were applied to test their suitability for establishing a chronology of arid-zone lacustrine sediments using a 5.88-m-long core drilled from Lake Ulaan, southern Mongolia.

Although the radiocarbon and OSL ages agree in some samples, the radiocarbon ages are older than the corresponding OSL ages at the 550-cm depth horizon (late Pleistocene) and in the 100–300-cm interval (early to late Holocene).

After about 50,000 years, the radiocarbon concentration remaining is too small to be measured for the purpose of radiocarbon dating. This is necessary to remove errors in raw radiocarbon dates caused by fluctuations in the amount of radiocarbon in the atmosphere in the past.

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