How did planetary differentiation create Earth’s core, mantle, and crust?

Planetary differentiation is the process by which Earth separated into chemically distinct layers—the core, mantle, and crust—following its accretion from the solar nebula approximately 4.56 billion years ago.1

Core Formation

As Earth grew, it was heated by the impacts of planetesimals and the gravitational energy released as dense materials sank. Iron, which makes up the bulk of the planet's metallic content, was reduced to a metallic state and sank toward the center to form the core. This high-density metallic liquid was immiscible with the surrounding silicate material, effectively segregating the core from the rest of the planet.23

Mantle and Crust Formation

The remaining material, primarily silicates (lithophile elements), formed the mantle. The crust subsequently formed through partial melting of the interior. During this process, less-dense liquids rose toward the surface and crystallized. Unlike the core's formation, which was driven by density-based metallic segregation, crustal formation resulted from geochemical sorting: minerals like olivine and pyroxene in the mantle rejected elements that did not fit their crystal structures, leading to a crust enriched in elements such as aluminum and alkali metals.34