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4.13: Earth's Core

Difficulty Level: At Grade Created by: CK-12
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Do you want to take a journey to the center of the earth?

Jules Verne's imagined core was fiery. But we know that the outer core is molten metal, as seen above. As hot as a journey to Verne's center of the earth might have been, a visit to the real location would be worse.

Core

At the planet’s center lies a dense metallic core. Scientists know that the core is metal because:

  1. The density of Earth's surface layers is much less than the overall density of the planet, as calculated from the planet’s rotation. If the surface layers are less dense than average, then the interior must be denser than average. Calculations indicate that the core is about 85% iron metal with nickel metal making up much of the remaining 15%.
  2. Metallic meteorites are thought to be representative of the core. The 85% iron/15% nickel calculation above is also seen in metallic meteorites ( Figure below ).

An iron meteorite is the closest thing to the Earth’s core that we can hold in our hands.

If Earth's core were not metal, the planet would not have a magnetic field. Metals such as iron are magnetic, but rock, which makes up the mantle and crust, is not.

Scientists know that the outer core is liquid and the inner core is solid because:

  1. S-waves stop at the inner core.
  2. The strong magnetic field is caused by convection in the liquid outer core. Convection currents in the outer core are due to heat from the even hotter inner core.

The heat that keeps the outer core from solidifying is produced by the breakdown of radioactive elements in the inner core.

Summary

  • Earth's core is dense metal.
  • The inner core is solid and the outer core is liquid, as indicated by seismic waves.
  • Metallic meteorites, density calculations, and the magnetic field are all clues that about the composition of Earth's inner and outer core.

Interactive Practice

Use this resource to answer the questions that follow.

1. What materials can P-waves travel through?

2. What materials can S-waves travel through?

3. How do we know the outer core is liquid?

4. What happens to P-waves when they go through a liquid?

5. What do P-waves tell about the inner core?

Review

1. Why is there convection in the outer core and what is the result of this?

2. If scientists discovered a major mistake in their calculations and Earth's crust turned out to be much denser than they'd thought, what would this say about the material that makes up the core?

3. What is the outer core so hot?

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Date Created:

Feb 24, 2012

Last Modified:

Jul 24, 2014
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