As we pointed out in these two articles, radiometric dates are based on known rates of radioactivity, a phenomenon that is rooted in fundamental laws of physics and follows simple mathematical formulas.
Natural processes absorb the equivalent of all natural emissions plus about 57% of man-made emissions, leaving an additional 16 billion metric tons of CO2 in the atmosphere each year. † In permafrost regions, perennial snow accumulations trap air bubbles that leave records of past airborne CO2 concentrations,   and because regional CO2 concentrations vary by less than 10 parts per million over the Earth, these local records are globally representative.  * Instruments located on satellites can measure certain properties of oxygen that vary with temperature.
A shellfish alive today in a lake within a limestone catchment, for instance, will yield a radiocarbon date which is excessively old.
The reason for this anomaly is that the limestone, which is weathered and dissolved into bicarbonate, has no radioactive carbon.
It involves the chemical reactions between chemical compounds in the atmosphere and chemical compounds on the planet's surface.
When your car's exhaust pipe falls apart noisily, it is because the steel from which it was constructed has, over several years, reacted with oxygen and rainwater to form rust. But that's a relatively fast example involving a relatively unstable compound.