1. Crust: There are two different types of crust: the oceanic crust (wich supports the ocean) and the continental crust (wich supports the continents). These two types of crust are made up of different types of rock. The thin oceanic crust is composed primarily of basalt. The thicker continental crust is composed primarily of granite.
2. Mantle: Mantle is composed mainly of olivine-rich rock. It has different temperatures at different depths. The temperature is lowest beneath the crust and increases with depth. The highest temperatures occur where the mantle material is in contact with the core. This steady increase of temperature with depth is known as the geothermal gradient. The geothermal gradient is responsible for different rock behaviors and the different rock behaviors are used to divide the mantle into two different zones. Rocks in the upper mantle are cool and brittle, while rocks in the lower mantle are hot and soft. Rocks in the upper mantle are brittle enough to break under stress and produce earthquakes. Rocks in the lower mantle are soft and flow when subjected to forces instead of breaking. 
3. Core: The core is composed mainly of iron and nickel. The core is Earth's source of internal heat because it contains radioactive materials which release heat as they break down into more stable substances. The core is divided into two different zones. The outer core and the inner core. The outer core is liquid because the temperatures are adequate to melt the iron-nickel alloy. The inner core is a solid even though its temperature is higher than the outer core. Tremendous pressure produced by the weight of the overlying rocks is strong enough to crowd the atoms tightly together and prevents the liquid state.

There are 2 other thin layers. These layers form part of 2 of the other 3 main layers:

1. Lithosphere: The lithosphere is the solid, rocky layer of the Earth. It is made by the crust and the upper mantle of Earth.
2. Asthenosphere: The asthenosphere is the weaker, hotter, and deeper part of the upper mantle. The pressure keeps it plastic, and it has a relatively low density. Seismic waves, pass relatively slowly through the asthenosphere.