Scientific instrument used for carbon dating
Libraries of tree rings of different calendar ages are now available to provide records extending back over the last 11,000 years.The trees often used as references are the bristlecone pine (Pinus aristata) found in the USA and waterlogged Oak (Quercus sp.) in Ireland and Germany.The science of dendrochronology is based on the phenomenon that trees usually grow by the addition of rings, hence the name tree-ring dating.Dendrochronologists date events and variations in environments in the past by analyzing and comparing growth ring patterns of trees and aged wood.These changes were brought about by several factors including, but not limited to, fluctuations in the earth’s geomagnetic moment, fossil fuel burning, and nuclear testing.The most popular and often used method for calibration is by dendrochronology.Tree rings provided truly known-age material needed to check the accuracy of the carbon-14 dating method.
At present, tree rings are still used to calibrate radiocarbon determinations.Nowadays, the internationally agreed upon calendar calibration curves reach as far back as about 48000 BC (Reimer et.al., INTCAL13 and Marine13 radiocarbon age calibration curves 0 – 50000 yrs cal BP, Radiocarbon 55(4), 2013).If a sample has the same proportion of radiocarbon as that of the tree ring, it is safe to conclude that they are of the same age.In practice, tree-ring calibration is not as straightforward due to many factors, the most significant of which is that individual measurements made on the tree rings and the sample have limited precision so a range of possible calendar years is obtained.
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For the period after 1950, a great deal of data on atmospheric radiocarbon concentration is available.