1. Earth’s Interior Evidence

2. 1. Density of the Earth
The strength of the gravitational pull of the Earth gives scientists a pretty good idea about the average density of the Earth.
If the whole Earth was made of rocks of crustal composition, it would not nearly be as dense as the Earth is, so the material beneath the crust must be more dense than the crust to make up for the difference.

3. 2. Earth’s Magnetic Field
Earth is a big magnet. This indicates that the center of the Earth must be made of magnetic elements like iron (Fe) and nickel (Ni).

4. 3. Evidence from Earthquakes
When seismic waves strike a new layer, some waves bounce off and go to the surface, and others continue through. Measuring how long it takes for the waves to travel to the new layer and back can tell scientists how deep the layer is.

6. Earthquakes, continued
S-waves cannot go through liquids. When earthquakes happen, s-waves from these earthquakes can be detected around the world except for a zone that is directly through the Earth from where the earthquake occurred. This indicates that a large part of the center of the Earth must be liquid.

7. Types of seismic waves:
S-waves = secondary waves (“wiggle” waves)
P-waves = primary waves (“push” waves)

9. 4. Rock Samples
Samples from the upper and middle crust have been collected through drilling, and samples from the crust and uppermost mantle have been collected from volcanic deposits. We have no samples from lower than that.
Mantle peridotite

10. 5. Meteorites
Meteorites give clues about what kinds of materials have been available in our solar system for making planets.
Most meteorites have lots of metal in them, so it is likely that the interior of the Earth is metallic too.