Radiometric dating is possible if
The fourth one is that we know what the concentration of atmospheric C14 was when the organism lived and died.
The story of radiocarbon dating shows science at its finest.
Many archaeological sites have been dated by applying radiocarbon dating to samples of bone, wood, or cloth found there. One is that the thing being dated is organic in origin.
If an element has more than one isotope present, and a mineral forms in a magma melt that includes that element, the element's different isotopes will appear in the mineral in precisely the same ratio that they occurred in the environment where and when the mineral was formed. The third and final axiom is that when an atom undergoes radioactive decay, its internal structure and also its chemical behavior change.
Losing or gaining atomic number puts the atom in a different row of the periodic table, and elements in different rows behave in different ways. Well, an atom's chemical activity pattern is a result of its electron shell structure.
However, after a few years a number of scientists got suspicious of this assumption, because dates obtained by the C14 method weren't tallying with dates obtained by other means.
A long series of studies of C14 content produced an equally long series of corrective factors that must be taken into account when using C14 dating.
Presented with a new method that gave answers different than existing methods, the scientists involved did not simply assume that either the old method or the new one was wrong.