The Earth!!!

The Earth has three layer. The core (inner and outer), the mantle and the crust.

The core consists of a fluid outer core and a solid inner core (the inner core, despite being very hot, is solid because of all the pressure it is under). Because the core contains iron and nickel, when it flows it generates a magnetic field. This is the source of the Earth's magnetic field! The core is about 3500 km wide.

The mantle makes up 82% of the Earths volume and is about 2900km. The mantle, like the core, is made up of two sections, the upper and the lower mantle. The upper mantle also has two sections to it, the lithosphere which is stiffer than the asthenosphere, which is the lower part. The lower mantle is very, very strong, as it has a lot of pressure on it.

The final layer is the crust and it too has two sections. One is the continental crust and the other is the oceanic crust. The oceanic crust is the top crust and is only 7km thick, which is a lot less than the other layers of the Earth. It is mostly made up of basalt, a dark igneous rock, that is commonly found on railway lines and tram lines. The continental crust sits underneath the oceanic crust and can vary between 35-70 km in depth.

http://scign.jpl.nasa.gov/learn/plate1.htm