definition radiometric dating - Absolute chronometric dating techniques

This is the only type of techniques that can help clarifying the actual age of an object.

Absolute dating methods mainly include radiocarbon dating, dendrochronology and thermoluminescence.

Indeed, carbon 14 (14C) is formed from the reaction caused by cosmic rays that convert nitrogen into carbon 14 and then carbon dioxide by combining with carbon 12 (12C) and carbon 13 (13C ), which are stable carbon isotopes.

Following the death of an organism, any exchange ceases and the carbon 14, which is radioactive and therefore unstable, slowly begins to disintegrate at a known rate (half-life of 5730 years, ie, after this period only half of the total carbon 14 present at the time of death remains).

The amount of carbon 14 remaining in the material to date is compared to a reference standard (ratio 14C/total carbon, 12C and 13C) to calculate the time elapsed since its occurrence.

A sample requires 10 to 20 grams of matter and usually consists of charred organic material, mainly charcoal, but bones (zooarchaeology) and shells can also be dated using this technique.

An initial reading dates the specimen which is then calibrated by considering this date and its correspondence with the measurable level of carbon 14 stored over time in the growth rings of certain tree species, including redwood and pine bristol.

The results of radiocarbon dating are expressed in years and include a time range (eg, 630± 60 BP).Several sets of rings from different trees are matched to build an average sequence.Subsequently, overlapping series of average sequences from trees that died at different times and come from various sources (ie, the wood of historic buildings, archaeological and fossil woods) are used to build a chronological sequence covering several hundred years which becomes a reference.However, this method is sometimes limited because the reoccupation of an area may require excavation to establish the foundation of a building, for instance, that goes through older layers.In this case, even if the foundation of the building is found in the same stratigraphic level as the previous occupation, the two events are not contemporary.Radiocarbon Dating Radiocarbon dating is the most widely used dating technique in archaeology.

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