Final answer:
The Earth has a dense crust, a less dense mantle, and a dense core.
Step-by-step explanation:
The Earth's interior consists of an inner and outer core, the mantle, and the crust. The inner core is very dense and solid, composed of an iron and nickel alloy. Surrounding the inner core is the liquid outer core, responsible for the Earth's magnetic field.
The mantle is less dense than the core and is a solid layer that can deform and flow slowly. The crust, the thin outer layer of the Earth, varies in thickness and density between continental and oceanic crust.