There is then a ratio of carbon-14 to carbon-12 in the bodies of plants, humans, and other animals that can fluctuate, but will be fixed at the time of death. The premise behind the method is to determine the ratio of carbon-14 left in organic matter, and by doing so, estimate how long ago death occurred by running the ratio backwards.
The second faulty assumption is that the rate of carbon-14 formation has remained constant over the years.
There are a few reasons to believe this assumption is erroneous.
The effect would be not unlike opening a can of soda and having the carbon dioxide fizzing out.
The water in these subterranean chambers would not have contained carbon-14, as the water was shielded from cosmic radiation.
The carbon-14 dioxide is utilized by plants in the same way normal carbon dioxide is.