Evolution of continental crust and sedimentary rock chemistry through time

The continental crust is the Earth's most evolved chemical reservoir. Over its 4-billion-year history, it has maintained an average andesitic composition. Secular trends in upper crustal chemistry arose because most of the Archean proto-continents had little topography, were submerged and repeatedly covered by Mg-rich lavas. With increasing chemical stratification and diminishing radioactive heat, continents became thicker and mechanically stronger and emerged, leading to stronger coupling with the exogenic spheres. By 2.5Ga, more diverse sediments (e.g., rich in Fe and U) were deposited and most volcanic gasses were emitted subaerially. Continental weathering formed clays and released nutrients and alkalinity into the ocean, strengthening the coupling of the C-cycle to the continents. Recycling of sediment then began to yield more diverse granites. Thick continental arcs were main players in Proterozoic crustal geochemistry but intraplate magmatism, and lower crustal remelting, have been a constant of the Earth's continents, regardless of prevailing tectonic regime.