The earth has 3 compositional layers as may already know. The first is the crust. It has a low density,silicate rock, 5-70km thick. The second layer is the maantel. It has high density, ultramafic silicate rock which can flow when subjected to long duration stresses. And now the last and final layer of the planet we live on is the core. It has iron and nickel,liquid outer region with a solid center.