The study by DePaolo and Wasserburg explores the isotopic variations of neodymium (Nd) and their implications for petrogenesis and Earth's history. The decay of samarium-147 (Sm-147) to neodymium-143 (Nd-143) allows the ratio of Nd-143 to Nd-144 to trace Sm/Nd fractionation in geological processes. Measurements of this ratio in terrestrial rocks reveal that the mantle has Sm/Nd similar to chondrites, suggesting a chondritic rare earth element (REE) distribution for Earth. However, variations in Nd-143/Nd-144 in the mantle indicate Sm/Nd heterogeneity and distinct mantle reservoirs. Oceanic tholeiites and alkali basalts have Sm/Nd higher than chondritic, indicating derivation from mantle sources with higher Sm/Nd. Alkali basalts cannot be derived from long-term light REE-enriched mantle reservoirs. The Sm-Nd system is useful for dating terrestrial rocks and provides insights into the chemical processes involved in rock formation. The ratio of Nd-143/Nd-144 is an indicator of changes in Nd abundance due to Sm-147 decay. The growth of this ratio in different reservoirs over time is influenced by Sm/Nd ratios. The study introduces a model to describe the evolution of Nd-143/Nd-144 in the Earth's mantle and crust, showing that the mantle has a uniform reservoir (UR) with a specific Nd-143/Nd-144 ratio. The initial Nd-143/Nd-144 ratio of a rock can be determined using this model. The study also discusses the implications of Nd isotopic variations for the Earth's history, showing that the Earth's Sm/Nd is similar to chondritic values within a few percent. Variations in Nd-143/Nd-144 in young basalts indicate isotopic heterogeneities in their source regions. The data suggest that mantle source regions with Sm/Nd different from chondritic values are not preserved for long periods. The crust has much lower Nd-143/Nd-144 ratios, reflecting its low Sm/Nd due to REE fractionation during crust formation. The study concludes that the Earth's Sm/Nd and REE abundance pattern are similar to chondritic meteorites. The Nd isotopic data provide insights into the Earth's mantle and crust evolution, showing that mantle sources have distinct Sm/Nd values and that the crust reflects its low Sm/Nd. The study also highlights the importance of the Sm-Nd system in understanding the Earth's geological history and the role of mantle heterogeneity in the formation of different rock types.The study by DePaolo and Wasserburg explores the isotopic variations of neodymium (Nd) and their implications for petrogenesis and Earth's history. The decay of samarium-147 (Sm-147) to neodymium-143 (Nd-143) allows the ratio of Nd-143 to Nd-144 to trace Sm/Nd fractionation in geological processes. Measurements of this ratio in terrestrial rocks reveal that the mantle has Sm/Nd similar to chondrites, suggesting a chondritic rare earth element (REE) distribution for Earth. However, variations in Nd-143/Nd-144 in the mantle indicate Sm/Nd heterogeneity and distinct mantle reservoirs. Oceanic tholeiites and alkali basalts have Sm/Nd higher than chondritic, indicating derivation from mantle sources with higher Sm/Nd. Alkali basalts cannot be derived from long-term light REE-enriched mantle reservoirs. The Sm-Nd system is useful for dating terrestrial rocks and provides insights into the chemical processes involved in rock formation. The ratio of Nd-143/Nd-144 is an indicator of changes in Nd abundance due to Sm-147 decay. The growth of this ratio in different reservoirs over time is influenced by Sm/Nd ratios. The study introduces a model to describe the evolution of Nd-143/Nd-144 in the Earth's mantle and crust, showing that the mantle has a uniform reservoir (UR) with a specific Nd-143/Nd-144 ratio. The initial Nd-143/Nd-144 ratio of a rock can be determined using this model. The study also discusses the implications of Nd isotopic variations for the Earth's history, showing that the Earth's Sm/Nd is similar to chondritic values within a few percent. Variations in Nd-143/Nd-144 in young basalts indicate isotopic heterogeneities in their source regions. The data suggest that mantle source regions with Sm/Nd different from chondritic values are not preserved for long periods. The crust has much lower Nd-143/Nd-144 ratios, reflecting its low Sm/Nd due to REE fractionation during crust formation. The study concludes that the Earth's Sm/Nd and REE abundance pattern are similar to chondritic meteorites. The Nd isotopic data provide insights into the Earth's mantle and crust evolution, showing that mantle sources have distinct Sm/Nd values and that the crust reflects its low Sm/Nd. The study also highlights the importance of the Sm-Nd system in understanding the Earth's geological history and the role of mantle heterogeneity in the formation of different rock types.