Evidence from coupled 147Sm–143Nd and 146Sm–142Nd systematics for very early (4.5-Gyr) differentiation of the Earth's 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 143Nd/144Nd 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 147Sm–143Nd systematics then suggests that primordial differentiation of the Earth may have begun ~4.5 Gyr ago. Here we present evidence for early differentiation, based on measurements of 143Nd/144Nd and 142Nd/144Nd ratios in a ~3.8-Gyr-old supracrustal rock from Isua, West Greenland. Coupled 146,147Sm–142,143Nd 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.