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For those researchers working in the field of human history, the chronology of events remains a major element of reflection.
Archaeologists have access to various techniques for dating archaeological sites or the objects found on those sites.
There are two main categories of dating methods in archaeology: indirect or relative dating and absolute dating.
Relative dating includes methods that rely on the analysis of comparative data or the context (eg, geological, regional, cultural) in which the object one wishes to date is found.
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).
It relies on a natural phenomenon that is the foundation of life on earth.
Crossdating is an important principle in dendrochronology.
It consists in comparing and matching two or more series of ring widths measured on different trees.
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).