EVIDENCE FROM COUPLED SM-147 ND-143 AND SM-146 ND-142 SYSTEMATICS FOR VERY EARLY (4.5-GYR) DIFFERENTIATION OF THE EARTHS MANTLE

THE volume of early Archaean crust that still survives today is very small (less than 1% of the present continental volume). This has been interpreted as indicating that crustal growth did not begin until about 4.0 Gyr ago, before which the silicate Earth remained well mixed and essentially undifferentiated. But the existence in some early Archaean rocks1-6 of inferred initial Nd-143/Nd-144 ratios higher than that of the bulk Earth suggests that by 3.8 Gyr ago the volume of the crust was as large as about 40% of the present value3,7,8. Given the apparently low rate of recycling in the Hadean era (that is, before 4 Gyr ago)7,8, consideration of Sm-147-Nd-143 systematics then suggests that primordial differentiation of the Earth may have begun approximately 4.5 Gyr ago. Here we present evidence for early differentiation, based on measurements of Nd-143/Nd-144 and Nd-142/Nd-144 ratios in a approximately 3.8-Gyr-old supracrustal rock from Isua, West Greenland. Coupled Sm-146, Sm-147-Nd-142, Nd-143 systematics suggest that fractionation of Sm/Nd took place 4.44-4.54 Gyr ago, owing to extraction of a light-rare-earth-element-enriched primordial crust.