Final answer:
The Earth's structure is arranged with denser materials at the center and less dense towards the surface, a process known as differentiation. The inner and outer core are very dense, and the mantle and crust become progressively less dense as one moves outward.
Step-by-step explanation:
The Earth's structure is organized such that denser materials are towards the center and less dense materials are towards the surface. This concept is known as differentiation, a process where a planet's materials sort themselves by density. The Earth's core, consisting of an inner core and outer core, is primarily made up of iron and nickel and is very dense. Surrounding the core is the mantle, which is less dense and has the ability to deform and flow slowly. The least dense layer, the crust, forms the Earth's surface.
By analyzing seismic wave patterns and Earth's bulk density compared to surface materials, scientists deduce that the heavy metals sank to form a dense core when the planet was once molten. The internal layers can also be characterized by their physical properties into the lithosphere (rigid) and asthenosphere (plastic or deformable).