Answer:
In the early part of the 20th century, geologists studied the vibrations (seismic waves) generated by earthquakes to learn more about the structure of the earth's interior. They discovered that it is made up of these distinct layers: the crust, the mantle, and the core.Geologists record the seismic waves and study how they travel through Earth. Different types of seismic waves behave differently. The speed of the waves and the paths they take reveal the structure of the planet. Using data from seismic waves geologists have learned that Earth's interior is made up of layers.