Rubidium strontium dating equation

The method is applicable to very old rocks because the transformation is extremely slow: the half-life, or time required for half the initial quantity of rubidium-87 to disappear, is approximately 50 billion years.

rubidium strontium dating equation-83

However, because this is a small number and counting atoms isn’t easy, it is more useful to use the ratio of one isotope to another.

By dividing the above equation by a common factor, a more useful equation can be created: This ratio of radiogenic strontium to a non-radiogenic isotope, Strontium-86, over time is more useful than the absolute amount of Strontium present in a sample.

Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.

All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus.

Different minerals in a given geologic setting can acquire distinctly different ratios of radiogenic strontium-87 to naturally occurring strontium-86 (Sr as the parent melt.

However, because Rb substitutes for K in minerals and these minerals have different K/Ca ratios, the minerals will have had different Rb/Sr ratios.

The utility of the rubidium-strontium isotope system results from the fact that Sr with a half life of 48.8 billion years.

In addition, Rb is a highly incompatible element that, during partial melting of the mantle, prefers to join the magmatic melt rather than remain in mantle minerals. The radiogenic daughter, Sr, is produced in this decay process and was produced in rounds of stellar nucleosynthesis predating the creation of the Solar System.

Sr is fairly incompatible in mafic systems and relatively incompatible in silica-rich systems.

This means that as partial melting occurs, Rb is going to partition to the melt in greater proportion than Sr will.

Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale.

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