Isotope decay dating
Radioactive decay is a natural process and comes from the atomic nucleus becoming unstable and releasing bits and pieces.
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.
This is a common dating method mainly used by archaeologists, as it can only date geologically recent organic materials, usually charcoal, but also bone and antlers.The relationship between the two is: T = 0.693 / λ Many different radioactive isotopes and techniques are used for dating.All rely on the fact that certain elements (particularly uranium and potassium) contain a number of different isotopes whose half-life is exactly known and therefore the relative concentrations of these isotopes within a rock or mineral can measure the age.However, potassium is very mobile during metamorphism and alteration, and so this technique is not used much for old rocks, but is useful for rocks of the Mesozoic and Cenozoic Eras, particularly unaltered igneous rocks.Argon-Argon dating (39Ar-40Ar) This technique developed in the late 1960s but came into vogue in the early 1980s, through step-wise release of the isotopes.
Another way of expressing this is the half-life period (given the symbol T).