Isochron radiometric dating wikipedia
At a certain temperature, the crystal structure has formed sufficiently to prevent diffusion of isotopes.
This temperature is what is known as closure temperature and represents the temperature below which the mineral is a closed system to isotopes.
Therefore, in any material containing a radioactive nuclide, the proportion of the original nuclide to its decay product(s) changes in a predictable way as the original nuclide decays over time.
While the moment in time at which a particular nucleus decays is unpredictable, a collection of atoms of a radioactive nuclide decays exponentially at a rate described by a parameter known as the half-life, usually given in units of years when discussing dating techniques.
Radiometric dating (often called radioactive dating) is a technique used to date materials, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates; and based on an observation of the relative quantities of the isotope and its daughter products.
It is the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself, and can be used to date a wide range of natural and man-made materials.
For example, a study of the Amitsoq gneisses from western Greenland used five different radiometric dating methods to examine twelve samples and achieved agreement to within 30 Ma on an age of 3,640 Ma.
Accurate radiometric dating generally requires that the parent has a long enough half-life that it will still be present in significant amounts at the time of measurement (except as described below under "Dating with short-lived extinct radionuclides"), the half-life of the parent is accurately known, and enough of the daughter product is produced to be accurately measured and distinguished from the initial amount of the daughter present in the material.
Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an isochron. In uranium-lead dating, the concordia diagram is used which also eliminates the problem of nuclide loss.