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Development of this process was aided by German chemists Otto Hahn and Fritz Strassmann, who later went on to discover nuclear fission in December 1938.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.The application of Sr isotope stratigraphy is generally limited to carbonate samples for which the Sr seawater curve is well defined.
This is well known for the Cenozoic time-scale but, due to poorer preservation of carbonate sequences in the Mesozoic and earlier, it is not completely understood for older sequences.Initial Nd ratios as well) the geological fingerprint of an object or skeleton can be measured, allowing migration patterns to be determined.