Early Silicate Earth Differentiation

The discovery of small Nd-142 anomalies in early Archean rocks has brought about a revolution in our understanding of early planetary differentiation processes. Nd-142 is a radiogenic isotope produced by the decay of now-extinct Sm-146 in crustal and mantle reservoirs. Given that Nd-142 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 Sm-147-Nd-143 and Sm-146-Nd-142 systems to ancient crustal rocks, to the more recent insights gained from application of Sm-146-Nd-142 to meteorites and lunar samples.