Minerals used in isotopic dating
This decay process leads to a more balanced nucleus and when the number of protons and neutrons balance, the atom becomes stable.
This radioactivity can be used for dating, since a radioactive 'parent' element decays into a stable 'daughter' element at a constant rate.
For an element to be useful for geochronology (measuring geological time), the isotope must be reasonably abundant and produce daughter isotopes at a good rate.
Either a whole rock or a single mineral grain can be dated.
The rate of decay (given the symbol λ) is the fraction of the 'parent' atoms that decay in unit time.
For geological purposes, this is taken as one year.
Another way of expressing this is the half-life period (given the symbol T).
The half-life is the time it takes for half of the parent atoms to decay.
These are released as radioactive particles (there are many types).
This technique uses the same minerals and rocks as for K-Ar dating but restricts measurements to the argon isotopic system which is not so affected by metamorphic and alteration events. The decay of 147Sm to 143Nd for dating rocks began in the mid-1970s and was widespread by the early 1980s.