C13 carbon dating
Instead scientist use an accelerator mass spectrometer to measure the ratio of the carbon-14 atoms to the carbon-12 atoms.A mass spec can do this easily with proper preparation.
The different isotopes of carbon do not differ appreciably in their chemical properties.
By counting tree rings and by correlating them with older tree rings (by matching up sequences of drought, etc.) we can go back about 8000 years.
We can do similar analysis with ice cores and varves.
Therefore, the percentages of the three isotopes will be the same in a living organism as it is in the organism’s environment.
Carbon-14 is not stable against beta-minus decay with a half-life of 5,730±40 years, but is constantly replenished in the atmosphere by cosmic ray interaction with nitrogen-14.