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# Earth's Inner Layers

## The crust, mantle and core are defined by composition; the lithosphere and asthenosphere from mechanical properties.

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Earth's Inner Layers

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 ).

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:

1. The crust is less than 1% of Earth by mass. The two types are oceanic crust and continental crust.
2. The mantle is hot, dense, dark (ultramafic) rock. It represents about 68% of Earth's mass.
3. 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 lessons.

### Layers by Mechanical Properties

Lithosphere and asthenosphere are divisions based on mechanical properties:

1. 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 lithosphere is made up of the crust and the uppermost mantle.
2. 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.

This animation shows the layers by composition and by mechanical properties: http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_layers.html .

### Vocabulary

• asthenosphere : Layer below the lithosphere, made of a portion of the upper mantle; the asthenosphere can flow.
• core : Innermost, densest layer of a celestial body.
• crust : Rocky outer layer of the Earth's surface.
• lithosphere : Layer of solid, brittle rock that makes up the Earth's surface.
• mantle : Middle layer of the Earth; made of hot rock.

### 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.

### Practice

Use the resource below to answer the questions that follow.

1. What is the core?
2. Explain the core's structure.
3. What is the mantle?
4. What is the crust?
5. Why does the Earth have layers?

### Review

1. What are the the layers of Earth based on composition. Where are they located?
2. What is the composition of the different layers?
3. How do the lithosphere and asthenosphere differ from each other?

### Vocabulary Language: English

asthenosphere

asthenosphere

Layer below the lithosphere, made of a portion of the upper mantle; the asthenosphere can flow.
core

core

Innermost, densest layer of a celestial body.
crust

crust

Rocky outer layer of the Earth's surface.
lithosphere

lithosphere

Layer of solid, brittle rock that makes up the Earth's surface.
mantle

mantle

Middle layer of the Earth; made of hot rock.