Early Silicate Earth Differentiation

The discovery of small ¹⁴²Nd anomalies in early Archean rocks has brought about a revolution in our understanding of early planetary differentiation processes. ¹⁴²Nd is a radiogenic isotope produced by the decay of now-extinct ¹⁴⁶Sm in crustal and mantle reservoirs. Given that ¹⁴²Nd heterogeneities can be produced only prior to 4.2 Gya, this short-lived chronometer provides selective information on the very early evolution of primordial silicate reservoirs. This information is particularly crucial for Earth, where the fingerprints of the earliest crustal formation processes have been almost entirely erased from the geological record. This article reviews the history of the field, from the pioneering applications of the ¹⁴⁷Sm-¹⁴³Nd and ¹⁴⁶Sm-¹⁴²Nd systems to ancient crustal rocks, to the more recent insights gained from application of ¹⁴⁶Sm-¹⁴²Nd to meteorites and lunar samples.