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samarium—neodymium dating The change from 147Sm to 143Nd is the result of alpha decay (147Sm has a half-life of 2.5 × 1011 years) and provides one of the newest methods of dating used in geochronology. The decay enriches the material in 143Nd relative to the stable isotope 144Nd. The ratio 143Nd: 144Nd that is measured is highly resistant to secondary processes of alteration and metamorphism. It can be used on terrestrial and extraterrestrial materials and gives valuable secondary information on petrogenesis in the crust and mantle.