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The Re-Os isotopic system was first developed in the early 1960s, but recently has been improved for accurate age determinations.
The main limitation is that it only works on certain igneous rocks as most rocks have insufficient Re and Os or lack evolution of the isotopes.
It is useful for dating very old igneous and metamorphic rocks and also meteorites and other cosmic fragments.The isotopes are then measured within the same machine by an attached mass spectrometer (an example of this is SIMS analysis).This is a common dating method mainly used by archaeologists, as it can only date geologically recent organic materials, usually charcoal, but also bone and antlers.This technique is used on ferromagnesian (iron/magnesium-containing) minerals such as micas and amphiboles or on limestones which also contain abundant strontium.However, both Rb and Sr easily follow fluids that move through rocks or escape during some types of metamorphism. The dual decay of potassium (K) to 40Ar (argon) and 40Ca (calcium) was worked out between 19.
The amount of 14C present and the known rate of decay of 14C and the equilibrium value gives the length of time elapsed since the death of the organism.