In contrast to the most simple radiometric dating techniques, isochron dating, which can be used for many isotopic decay sequences (e.g.
rubidium-strontium decay sequence), does not require knowledge of the initial proportions.
Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances.
It is our principal source of information about the age of the Earth and a significant source of information about rates of evolutionary change.
All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus.
When a material incorporates both the parent and daughter nuclides at the time of formation, it may be necessary to assume that the initial proportions of a radioactive substance and its daughter are known.