Radio-isotopic dating is the determination of ages of geologic materials through the comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates.
D = D0 + N(eλt − 1)
- t is age of the sample,
- D is number of atoms of the daughter isotope in the sample,
- D0 is number of atoms of the daughter isotope in the original composition,
- N is number of atoms of the parent isotope in the sample, and
- λ is the decay constant of the parent isotope, equal to the inverse of the radioactive half-life of the parent isotope times the natural logarithm of 2.