Early Silicate Earth Differentiation

Abstract

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