Figure 1. An iron meteorite is the closest thing to the Earth’s core that we can hold in our hands.

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 1).

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 do not go through the outer 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.

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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?

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