The decay of 147Sm to 143Nd allows the 143Nd/144Nd ratio to be used as a tracer for Sm/Nd fractionation in long-term geological processes. The study investigates the isotopic composition of Nd in terrestrial rocks to understand its implications for petrogenesis and the history of the Earth's crust and mantle. The results show that the majority of the mantle's Nd isotopic composition is similar to that of chondrites, suggesting a chondritic REE distribution for the Earth. However, variations in 143Nd/144Nd exist in the mantle, indicating Sm/Nd heterogeneity and distinct reservoirs with characteristic 143Nd/144Nd ratios. Oceanic tholeiites and alkali basalts are derived from sources with Sm/Nd 5-10% higher than chondrites over the age of the Earth. Alkali basalts cannot be derived from long-term light REE-enriched mantle reservoirs. The Sm-Nd system is useful for dating terrestrial rocks, and the authors discuss its potential in DePaolo (1976). The analytical procedures and data are detailed, including the separation of Sm and Nd using cation exchange resin and mass spectrometric measurements. The data are presented normalized to a uniform reservoir (UR) and show that the Earth's Sm/Nd is close to that of chondrites, with variations indicating the existence of isotopic heterogeneities in young basalts and the preservation of significant heterogeneities in the mantle for ~1-4 billion years. The crustal material has much lower 143Nd/144Nd than the mantle, reflecting REE fractionation during crust formation.The decay of 147Sm to 143Nd allows the 143Nd/144Nd ratio to be used as a tracer for Sm/Nd fractionation in long-term geological processes. The study investigates the isotopic composition of Nd in terrestrial rocks to understand its implications for petrogenesis and the history of the Earth's crust and mantle. The results show that the majority of the mantle's Nd isotopic composition is similar to that of chondrites, suggesting a chondritic REE distribution for the Earth. However, variations in 143Nd/144Nd exist in the mantle, indicating Sm/Nd heterogeneity and distinct reservoirs with characteristic 143Nd/144Nd ratios. Oceanic tholeiites and alkali basalts are derived from sources with Sm/Nd 5-10% higher than chondrites over the age of the Earth. Alkali basalts cannot be derived from long-term light REE-enriched mantle reservoirs. The Sm-Nd system is useful for dating terrestrial rocks, and the authors discuss its potential in DePaolo (1976). The analytical procedures and data are detailed, including the separation of Sm and Nd using cation exchange resin and mass spectrometric measurements. The data are presented normalized to a uniform reservoir (UR) and show that the Earth's Sm/Nd is close to that of chondrites, with variations indicating the existence of isotopic heterogeneities in young basalts and the preservation of significant heterogeneities in the mantle for ~1-4 billion years. The crustal material has much lower 143Nd/144Nd than the mantle, reflecting REE fractionation during crust formation.