Samarium–neodymium dating
Samarium–neodymium dating uses the decay of samarium-147 to neodymium-143, well suited to igneous meteorites.
Samarium–neodymium dating uses samarium-147, which decays to neodymium-143 with a half-life of about 106 billion years. Both are rare earth elements, which behave similarly in chemistry and resist being moved by weathering or mild heating. This makes the system robust.
Ages are found with isochrons from minerals such as pyroxene, plagioclase and phosphates, which take up samarium and neodymium in different proportions. The method is especially useful for basaltic meteorites such as shergottites, eucrites and lunar basalts. It also has a short-lived partner: samarium-146, now extinct, decayed to neodymium-142 with a half-life of roughly 100 million years and is used to study early differentiation of Earth, the Moon and Mars.
Neodymium isotopes also act as tracers. They reveal whether a magma came from a part of the mantle that had previously lost or gained rare earth elements. Martian shergottites, for instance, fall into groups with distinct neodymium signatures from different mantle sources.
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