2018 Volume 127 Issue 5 Pages Cover05_01-Cover05_02
The cover art is a schematic illustration showing the evolution of the inner earth during the Hadean. The dry Earth was formed at 4.55 Ga. By 4.53 Ga, the mantle had solidified to form a layered structure and stagnant lid tectonics operated. Between 4.37 and 4.20 Ga, the ABEL Bombardment progressed to deliver atmospheric and oceanic components onto the dry Earth. Due to the destruction of the stagnant lid by huge impactors, stagnant lid tectonics transitioned to plate tectonics. By 4.30 Ga, the bi-modal lithosphere (continental crust and oceanic crust) appeared following bombardment to operate plate tectonics. Due to tectonic erosion, the primordial continents (anorthosite, komatiite, and KREEP I basalt) were transported into the deep mantle. The densest KREEP I basalt dripped down to the bottom of the mantle and accumulated (almost all KREEP I basalt should have accumulated at CMB by 4.0 Ga) (Maruyama et al., 2018).