The evolution of Earth’s early continental crust

Abstract

Continental crust is fundamental to planetary habitability, providing the geochemical reservoirs and physical interfaces that drive and regulate exchanges among the atmosphere, hydrosphere and biosphere. However, the evolution of Earth’s crust is uncertain owing to debate regarding the competing roles of internal versus external energetic drivers. In this Review, we examine the interplay between internal and external drivers of the production, modification and destruction of crust on the early Earth using geochemical, geological and geophysical data. Internal drivers are potentially linked to plate tectonics and processes such as subduction (dripping) or delamination. External drivers from large meteorite impacts likely influenced crust formation by inducing rapid decompression melting of the mantle to form basaltic protocratons, the early, mantle-derived crustal nuclei that preceded stable continental crust. On a planet covered by water, protocratons might have been transformed by intracrustal differentiation into evolved (continental) crust. Future research into the processes driving Earth’s early evolution and habitability should consider a wide range of temporal and spatial scales from seconds to millions of years and the subgrain to the galactic, to uncover the long-wavelength patterns, in mantle overturn rates and impact flux preserved in deep-time records. Continental crust is important for Earth’s habitability. This Review explores how the formation and stabilization of Earth’s early continental crust was modulated by internal and external factors such as subduction and bolide impacts, respectively.