Rubidium–strontium dating
Rubidium–strontium dating uses the slow decay of rubidium-87 to strontium-87, usually with an isochron.
Rubidium–strontium dating uses rubidium-87, which decays to strontium-87 with a half-life of about 49 billion years, more than ten times the age of the Universe. The decay is so slow that measurable changes take a long time, which suits ancient rocks.
The method usually works by isochron. Several minerals or pieces of a rock with different rubidium-to-strontium ratios are measured. If they formed together, their isotopes fall on a straight line, and the slope gives the age. The line's starting point also reveals the initial strontium isotope ratio, which shows how much the source had evolved.
In meteoritics, rubidium–strontium was historically important: early measurements in the 1960s on chondrites and achondrites gave ages near 4.5 billion years, supporting the idea that meteorites date the formation of the Solar System. Today it is used particularly for Martian and lunar rocks. Rubidium is a volatile element, so the method also tracks volatile loss from early bodies.
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