These samples have 
to be organic matter (i.e., wooden, bones, and shells) or certain minerals and geologic material that include radioactive isotopes. The rate of decay for lots of radioactive isotopes has been measured; neither warmth, strain, gravity, nor other variables change the rate of decay. Carbon‑14 is important for archaeology because it’s common in archaeological deposits.
Below are a variety of the decay series that are commonly used in radiometric relationship of geological samples. The next step in radiometric relationship involves changing the number of half-lives which have passed into an absolute (i.e., actual) age. This is finished by multiplying the number of half-lives which have passed by the half-life decay constant of the father or mother atom (again, this worth is determined in a laboratory).