Mafic rocks of the Ukaliq supracrustal belt display negative 142Nd anomalies.
BIFs interleaved in the sequence show no evidence for in situ decay of 146Sm.
142Nd anomalies are likely inherited from a metasomatically enriched mantle source.
Sm–Nd systematics imply preservation of Earth's protocrust for >600 Myr.
This suggests inefficient lithospheric recycling in the post magma ocean Earth.