What are two types of evidence geologists use to learn about the earth's interior?

To learn about the Earth's interior, geologists use two main types of evidence:
1) Direct evidence from rock samples, and
2) Indirect evidence from seismic waves.
Rock samples are obtained by drilling deep holes into the ground. These samples are then used to obtain more information about the rock structures underneath the ground surface. Sometimes, the samples are also obtained through volcanic activity (which may cause the rocks from deep underground to be brought to the surface). However, such direct evidence-based investigation is limited to samples obtained from only a few kilometers underneath the Earth's surface.
Geologists can also use seismic waves as indirect evidence to study the interior of our planet. Geologists keep track of seismic activity and record seismic waves and then study the paths taken by these waves as an indirect measure of Earth's interior. Based on such indirect evidence, geologists have found that our planet is made up of several layers.
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