Question: How do people know exactly what the inside of the earth looks like if no one has ever been down there?

Clare Devery answered on 9 Mar 2015:

Excellent question! You’re right, we certainly can’t go there! I’m pretty sure the deepest mines from the Earth’s surface only go about a mile into the ground…which isn’t relatively very far at all. So, there needs to be a different way of finding out, other than gathering real physical samples.
Scientists (mainly geoscientists) use waves to study the different layers of the earth. Usually the waves are seismic waves, which are waves generated by earthquakes. The seismic waves are bent, sped up, or slowed down, or even reflected when they pass through the earth’s layers. Different types of materials (liquid/solid/gas) determine the speed of the waves. Bending of the waves occurs at the layer’s boundaries. So by studying these seismic waves, we can determine information about what may be underneath us.

The principle is very much like watching ripples in water. If you throw a rock into a swimming pool, with a brick wall on one side of it and just water on the other, you will see that the waves generated behave very differently on either side of the rock’s entry point. Even if you couldn’t actually see the brick wall, by just studying the ripples you could determine that there was something obstructing the wave’s path.

So, no one knows what it looks like for sure, because no one has seen it. But we can make fairly good guesses based on what the science has predicted is down there! I hope this answers your question!