Briefly describe the formation of our density stratified Earth.

The planet grew by the aggregation of particles. Meteors and asteroids bombarded the surface, heating the new planet and adding to its growing mass. At the time, Earth was composed of a homogenous mixture of materials. Earth lost volume because of gravitational compression. High temperatures in the interior turned the inner Earth into a semisolid mass; dense iron and nickel fell toward the center to form the core, while less dense silicates moved outward. Friction generated by this movement heated the Earth even more. The result of density stratification is evident in the formation of the inner and outer core, the mantle, and the crust.