How do we know that the Earth has layers, and how do we know what elements make up each of the layers?

Question

How do we know that the Earth has layers, and how do we know what elements make up each of the layers?

In: 10

Answer 1

IIRC, the different layers have different densities that refract the waves from earthquakes in different ways. Studying this phenomenon allows you to infer the composition from the densities required to refract the waves.