So what do we know about the formation and structure of the Earth?

We know that Earth, like the other planets in our solar system, cooled from a hot, molten body into a solid, layered planet, but how do we know about the internal structure of the Earth? We can find out by 'seeing' inside the Earth using the echoes from earthquakes.

In the early 20th century, geologists studied the seismic waves (vibrations) resulting from earthquakes and this led to the discovery that the Earth is made up of three distinct layers (Holden 2012: 30):

• The crust (rigid)
• The mantle (plastic / rigid)
• The core (liquid / rigid)