WHY is Earth structured the way it is?

It was the first discovery of a major change in the Earth's structure as one goes deeper. The crust is the outermost layer of the Earth. It is made of solid rocks. It is mostly made of the lighter elements, silicon, oxygen, aluminium.

During the next major phase of earth's formation cooling and differentiation of the Earth's layers occurred. Dense materials sank to the center, forming an iron-nickel rich core. Lighter buoyant silicate-rich magma rose to the surface.