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The only problem is that we only know the number of daughter atoms now present, and some of those may have been present prior to the start of our clock. The reason for this is that Rb has become distributed unequally through the Earth over time.We can see how do deal with this if we take a particular case. For example the amount of Rb in mantle rocks is generally low, i.e. The mantle thus has a low If these two independent dates are the same, we say they are concordant.In contrast, Earth’s most abundant lava rocks, which represent the mantle and make up the major oceanic ridges, have values between 0.703 and 0.705.This difference may appear small, but, considering that modern instruments can make the determination to a few parts in 70,000, it is quite significant.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.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.Each of these minerals has a different initial rubidium/strontium ratio dependent on their potassium content, the concentration of Rb and K in the melt and the temperature at which the minerals formed.

During fractional crystallization, Sr tends to be come concentrated in plagioclase, leaving Rb in the liquid phase.

Strata Data has for many years offered a strontium isotope dating service to the petroleum industry in collaboration with Isotopic Ltd.

Strontium isotope stratigraphy is now an established technique which provides a numerical age related to a global scale based on the Sr ratio of past seawaters.

During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase.

Therefore, given sufficient time for significant production (ingrowth) of radiogenic For example, consider the case of an igneous rock such as a granite that contains several major Sr-bearing minerals including plagioclase feldspar, K-feldspar, hornblende, biotite, and muscovite.

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