This “spike” is added to the sample prior to digestion to ensure full spike-sample equilibrium.
In recent years, the Rb–Sr dating technique has lost some of its popularity to other dating tools.
Other chronometers, such as U–Pb in zircon, can, in principle, date similar events to higher precision and, in the case of high-temperature igneous emplacement events, higher accuracy.
Sr, where the unstable Rb-87 isotope is referred to as the parent nuclide, being approximately 27 % of all rubidium.
The daughter nuclide (Sr-87) is represented by Sr-86, which is stable and not subject to radiogenic ingrowth and constitutes approximately 9.9 % of all strontium.
To directly compare Sr isotope compositions of these phases, irrespective of their absolute amount of Rb and Sr, all Sr-87 values are reported relative to a stable Sr isotope (Sr-86) that is not subject to radiogenic ingrowth.
Thus, all Sr isotope compositions are reported as the atomic mass, and [ppm] the concentration of a species, usually given in parts per million.
This makes the Rb–Sr dating technique, in principle, suitable to date samples from the infant stages of the solar system to very recent igneous events, i.e., a few million years before present.
For dating with the Rb–Sr technique, at least two phases (either whole rocks or minerals) with different Rb–Sr ratios are required.
Subsequent improvements in precision and accuracy have contributed significantly to a better understanding of Earth’s history.
With the advent and distribution of mass spectrometers, the Rb–Sr technique has become the most important tool in dating igneous rocks throughout Earth’s history and to the infant stages of the solar system.
: Common expression of the intercept of the isochron with the ordinate in a Nicolaysen diagram that marks the strontium isotope composition at the time of formation which, by definition, is that of all phases contributing to the isochron.