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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.To get to that point, there is also a historical discussion and description of non-radiometric dating methods.

These are often characterised as the norm, rather than the exception.Together with stratigraphic principles, radiometric dating methods are used in geochronology to establish the geological time scale.Among the best-known techniques are radiocarbon dating, potassium-argon dating and uranium-lead dating.During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase.Hence, the Rb/Sr ratio in residual magma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. Typically, Rb/Sr increases in the order plagioclase, hornblende, K-feldspar, biotite, muscovite.

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