147Sm143Nd

147Sm-143Nd refers to a radiometric dating system based on the decay of samarium-147 to neodymium-143. Samarium-147 is a naturally occurring radioisotope that decays by alpha emission to neodymium-143 with a half-life of about 1.06 × 10^11 years. The decay lowers the mass number by four and the atomic number by two, producing Nd-143 as the daughter nuclide. Because Nd-143 is stable, the accumulating daughter can be measured to infer the age of the material.

Natural occurrence and significance: Samarium is a rare earth element present in various minerals. Among its isotopes, Sm-147 provides a long-lived clock suitable for dating geological materials. The Sm-Nd system is widely used in geochronology and cosmochemistry to investigate the timing of crustal formation, mantle differentiation, and planetary accretion processes. Variations in the Nd isotopic composition of rocks reflect their Sm/Nd history and source characteristics.

Dating method and interpretation: In practice, scientists measure the isotopic ratios 143Nd/144Nd and 147Sm/144Nd in minerals. Since 143Nd increases over time as Sm-147 decays, plotting these ratios for different mineral fractions yields an isochron. The slope gives the age since the system closed and differentiated, while the intercept relates to the initial Nd isotopic composition. This method relies on closed-system behavior and knowledge of initial isotopic ratios; it is often used alongside other dating approaches to constrain geological timelines.

Applications and limitations: The 147Sm-143Nd system is valuable for dating old rocks, meteorites, and planetary differentiation events. Limitations include potential disturbance of Sm-Nd system by metamorphism or melting, and uncertainties in initial Nd isotopic compositions. Nevertheless, it remains a cornerstone technique in earth and planetary sciences.