1. Laboratoire de Géochimie et Cosmochimie (UMR 7579 CNRS), Institut de Physique du Globe de Paris, Université Denis Diderot 4, place Jussieu,75252 Paris Cedex 05, France
2. Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, UK

Correspondence to: Guillaume Caro¹ Correspondence and requests for materials should be addressed to G.C. (Email: caro@ipgp.jussieu.fr).

Abstract

Application of the ¹⁴⁷Sm–¹⁴³Nd chronometer (half-life of 106 Gyr) suggests that large-scale differentiation of the Earth's mantle may have occurred during the first few hundred million years of its history¹. However, the signature of mantle depletion found in early Archaean rocks is often obscured by uncertainties resulting from open-system behaviour of the rocks during later high-grade metamorphic events². Hence, although strong hints exist regarding the presence of differentiated silicate reservoirs before 4.0 Gyr ago, both the nature and age of early mantle differentiation processes remain largely speculative^{3, 4, 5}. Here we apply short-lived ¹⁴⁶Sm–¹⁴²Nd chronometry (half-life of 103 Myr) to early Archaean rocks using ultraprecise measurement of Nd isotope ratios. The analysed samples are well-preserved metamorphosed sedimentary rocks from the 3.7–3.8-Gyr Isua greenstone belt of West Greenland. Our coupled isotopic calculations, combined with an initial _¹⁴³Nd value from ref. 6, constrain the mean age of mantle differentiation to 4,460 115 Myr. This early Sm/Nd fractionation probably reflects differentiation of the Earth's mantle during the final stage of terrestrial accretion.