7.1 Earth’s Layers

What’s below our feet? What’s way below?

If we could cut Earth open, we’d see the inner core at the center, then the outer core, the mantle in the middle and the crust on the outside. If you are talking about plates, though, there’s 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, 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.

Layers by Mechanical Properties

Lithosphere and asthenosphere are divisions based on mechanical properties:

  1. The lithosphere is composed of both the crust and the portion of the upper mantle and behaves as a brittle, rigid solid.
  2. The asthenosphere is partially molten upper mantle material and behaves plastically and can flow.

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

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.
  • Continental crust is felsic, oceanic crust is mafic, the mantle is ultramafic, and the core is metallic.

Interactive Practice

Use this resource to answer the questions that follow.

http://www.learner.org/interactives/dynamicearth/structure.html

1. What substances make up the inner core?

2. What is the structure of the inner core?

3. What is the structure of the outer core?

4. Explain the composition of the mantle.

5. What is the asthenosphere?

Review

1. What are the the layers of Earth based on composition and where are they located?

2. What is the composition of the different layers?

3. How do the lithosphere and asthenosphere differ from each other?

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