Either a whole rock or a single mineral grain can be dated.Some techniques place the sample in a nuclear reactor first to excite the isotopes present, then measure these isotopes using a mass spectrometer (such as in the argon-argon scheme).
This radioactivity can be used for dating, since a radioactive 'parent' element decays into a stable 'daughter' element at a constant rate.
The rate of decay (given the symbol λ) is the fraction of the 'parent' atoms that decay in unit time.
The half-life is the time it takes for half of the parent atoms to decay.
The relationship between the two is: T = 0.693 / λ Many different radioactive isotopes and techniques are used for dating.
This method is useful for igneous and metamorphic rocks, which cannot be dated by the stratigraphic correlation method used for sedimentary rocks. Some do not change with time and form stable isotopes (i.e.
those that form during chemical reactions without breaking down).
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.
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.
measurement, measuring, mensuration, measure - the act or process of assigning numbers to phenomena according to a rule; "the measurements were carefully done"; "his mental measurings proved remarkably accurate" techniques to precisely measure the age of the eruptions of the Kalkarindji volcanic province where lavas covered an area of more than 2 million square kilometers in the Northern Territory and Western Australia.
Radioactive dating is a method of dating rocks and minerals using radioactive isotopes.
This technique also helps in determining the composition and evolution of the Earth's mantle and bodies in the universe.