Magmas are formed by partial melting of silicate rocks either in Earth’s mantle or the continental crust. Primary magmas from Earth’s mantle are basaltic in composition, and form the oceanic crust and part of the continental crust. Through the history of Earth, mantle magmas and their differentiation products represent juvenile additions from the mantle to crust, and thus the formation and differentiation of magmas is the underlying process in the formation of the continents on which we live.