The advantage of isochron dating as compared to simple radiometric dating techniques is that no assumptions are needed about the initial amount of the daughter nuclide in the radioactive decay sequence.Indeed, the initial amount of the daughter product can be determined using isochron dating.
It can be used to date rocks that formed from about 1 million years to over 4.5 billion years ago with routine precisions in the 0.1–1 percent range.
Samarium-neodymium dating is useful for determining the age relationships of rocks and meteorites, based on radioactive decay of a long-lived samarium (Sm) isotope to a radiogenic neodymium (Nd) isotope.
Nd isotope ratios are used to provide information on the source of igneous melts as well as to provide age data.
The greater the initial concentration of the parent, the greater the concentration of the radiogenic daughter isotope will be at some particular time.
Thus, the ratio of the daughter to non-radiogenic isotope will become larger with time, while the ratio of parent to daughter will become smaller.