3.16: Earth's Inner Layers

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What's below our feet? What's way below?

If we could cut Earth open, we'd see the following layers from inside to outside: inner core, outer core, mantle, and crust. Alternatively, you can think of the brittle lithosphere riding on the plastic asthenosphere. Whew!

Layers by Composition

The layers scientists recognize are pictured below (Figure below).

Composition of Earth's layers

A cross section of Earth showing the following layers: (1) crust (2) mantle (3a) outer core (3b) inner core (4) lithosphere (5) asthenosphere (6) outer core (7) inner core.

Core, mantle, and crust are divisions based on composition:

The crust is less than 1% of Earth by mass. The two types are oceanic crust and continental crust.
The mantle is hot, dense, dark (ultramafic) rock. It represents about 68% of Earth's mass.
The core is mostly iron metal. The core makes up about 31% of the Earth. Earth's metallic core has two layers: a solid inner layer and a liquid outer layer.

The terms core, mantle, and crust will be described in more detail in the next three concepts.

Layers by Mechanical Properties

Lithosphere and asthenosphere are divisions based on mechanical properties:

The lithosphere is composed of both the crust and the uppermost mantle. The lithosphere is a brittle, rigid solid. It is easily cracked or broken.
The asthenosphere is below the lithosphere. The asthenosphere is also in the upper mantle. This layer is solid, but it can flow and bend. A solid that can flow is like silly putty.

Summary

By composition, Earth is divided into core, mantle, and crust.
By mechanical properties, the crust and upper mantle are divided into lithosphere and asthenosphere.
The core-mantle-crust divisions are based on composition.
The lithosphere-asthensophere divisions are based on mechanical properties.