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Tree ring dating reliability
Plants obtain all their carbon atoms from the atmosphere.
The atmosphere contains many stable carbon atoms and relatively few radiocarbon atoms.
The ratio of radiocarbon to stable carbon atoms in the atmosphere has varied in the past.
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.
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.
Radiocarbon dating works by precisely measuring the ratio of radiocarbon to stable carbon in a sample. The tree-ring chronologies have been constructed by counting the annual rings in living trees and matching patterns in these rings to older wood and dead trees.
2010CB951001), Meteorology Public welfare Industry Research Special project (GYHY201106013, GYHY200806011), the basic research project of science and technology ministry of China (2007FY220200), NSFC Project (No.
40975056, 41071072, 41005059), China Desert Meteorological Science Research Foundation (SQJ2010011), the Foundation of Xinjiang Laboratory of Tree-ring Ecology (XJYS0911-2009-01).