The Earth has four main layers, from the innermost to the outermost:

• Inner core: The solid center of the Earth, composed mainly of iron and nickel.
• Outer core: A liquid layer surrounding the inner core, also made mostly of iron and nickel.
• Mantle: A thick layer of hot, dense rock between the core and the crust.
• Crust: The thin, solid outermost layer of the Earth where we live.

These four layers are the most commonly recognized major divisions of Earth's internal structure

. Additionally, these layers can be subdivided further. For example, the mantle is sometimes divided into upper and lower parts, and the crust can be classified into oceanic and continental types. The lithosphere includes the crust and the uppermost mantle, and below it lies the asthenosphere, a softer, semi-molten layer of the upper mantle

. In summary, Earth is generally described as having four primary layers, but more detailed models identify up to seven layers when including subdivisions like lithosphere and asthenosphere. The basic four-layer model remains the standard for understanding Earth's structure.