Answers to radiometric dating assignment
(Note that this doesn't mean the half-life of an element is a constant.
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.
When we know how much has decayed, we know how old the sample is.
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.
The second assumption is that the organism in question got its carbon from the atmosphere.