Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite

• Ultrahigh pressure (UHP) eclogite is absent from the rock record before c. 0.6 Ga. Continental crust (CC) has experienced secular change, becoming more felsic with time. Mafic Archean CC becomes too dense to exhume UHP conditions are reached. More mafic would have been submerged by a global ocean 1.3 km deep. Implications for hypotheses requiring subaerial land emergence of life. The absence ultrahigh orogenic in geological older than Ga problematic evidence subduction having begun on Earth during (4.0–2.5 Ga). Many eclogites Phanerozoic and Proterozoic terranes occur as boudins encased within low-density crust, which provides positive buoyancy subduction; however, recent geochemical proxy analysis shows that continental was previously thought, greater proportions basalt komatiite modern-day continents. Here, we show via petrological modelling change petrology bulk composition upper make negatively buoyant mantle reaching conditions. Subducted or delaminated passes point no return metamorphism prior stabilization coesite, while remain positively at these depths. may thus readily formed Earth, but could not exhumed, weakening arguments Neoproterozoic onset plate tectonics. Further, isostatic balance calculations continents indicate early covered over 1 deep, corroborating independent isotopic large-scale earlier 3 Our findings weaken life likely emerged shallow ponds, instead support involving development hydrothermal vents deep ocean.