Use of radiocarbon dating
This is the “half-life.” So, in two half-lives, or 11,460 years, only one-quarter of that in living organisms at present, then it has a theoretical age of 11,460 years.Anything over about 50,000 years old, should theoretically have no detectable C.
A stronger magnetic field deflects more cosmic rays away from the Earth.
This also has to be corrected for. Second, the ratio of C in the atmosphere at that time to be estimated, and so partial calibration of the “clock” is possible.
Accordingly, carbon dating carefully applied to items from historical times can be useful.
However, even with such historical calibration, archaeologists do not regard C produced and therefore dating the system.
The amount of cosmic rays reaching the Earth varies with the sun's activity, and with the Earth's passage through magnetic clouds as the solar system travels around the Milky Way galaxy.
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That is, they take up less than would be expected and so they test older than they really are.