Neodymium-142 data for rocks from the Nuvvuagittuq greenstone belt in northern Quebec, Canada, show that some rock types have lower 142 Nd/ 144 Nd ratios than the terrestrial standard (ϵ 142 Nd = –0.07 to –0.15). Within a mafic amphibolite unit, 142 Nd/ 144 Nd ratios correlate positively with Sm/Nd ratios and produce a 146 Sm- 142 Nd isochron with an age of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(4280_{-81}^{+53}\) \end{document} million years. These rocks thus sample incompatible-element-enriched material formed shortly after Earth formation and may represent the oldest preserved crustal section on Earth.