Radiometric dating parent daughter isotopes

The Re-Os isotopic system was first developed in the early 1960s, but recently has been improved for accurate age determinations.

The main limitation is that it only works on certain igneous rocks as most rocks have insufficient Re and Os or lack evolution of the isotopes.

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.

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.

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.

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.

Radiocarbon dating is normally suitable for organic materials less than 50 000 years old because beyond that time the amount of 14C becomes too small to be accurately measured.

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