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.