Radio 14 carbon 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.
This will make old things look older than they really are.
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.
Also, the Genesis flood would have greatly upset the carbon balance.
The flood buried a huge amount of carbon, which became coal, oil, etc., lowering the total C ratio in plants/animals/the atmosphere before the flood had to be lower than what it is now.
So, we have a “clock” which starts ticking the moment something dies.