Bone dating methods

The partial overlap of sets of trees that died at different times allows the construction of average chronological sequences (courtesy Groupe de recherche en dendrochronologie historique; illustration C.Dagneau)Wall where the Gore Creek skeleton bones were found in 1975, in a gully located near Pritchard, BC. Helens Y tephra (ash) dated at 3200 years BP, and the lower white line is from the Mount Mazama eruption that took place almost 7000 years ago (courtesy Jerome Cybulski).Stratigraphy Inspired by geology, stratigraphy uses the principle of the superposition of strata which suggests that, in a succession of undisturbed SOILS, the upper horizons are newer than the lower ones.Generally, each stratum is isolated in a separate chronological unit that incorporates artifacts.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).

Archaeologists have access to various techniques for dating archaeological sites or the objects found on those sites.Dendrochronology Dendrochronology is a method that studies the rings of tree trunks to define characteristic sequences by analyzing the morphology of growth rings for a given species.This method is based on the principle that the variation in tree growth from one year to another is influenced by the degree of precipitation, sunshine, temperature, soil type and all ambient conditions and that, consequently, reference patterns can be distinguished.Crossdating is an important principle in dendrochronology.It consists in comparing and matching two or more series of ring widths measured on different trees.

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