The surface layer of the Earth is around 30 miles deep (i.e. clay, dirt, rocks, etc.). Next, is the mantle which is 1,800 miles deep. The upper section of the mantle is made of mostly iron and nickel and has a temperature of around 400 degrees. The lower section of the mantle is some type of plastic liquid and it's 4,500 degrees. The mantle is constantly moving due to convection currents which basically means there's so much heating and cooling going on because of the different temperatures of the mantel's layers, that its liquids are always in a state of flux.
At the center of our plant is the Earth's core. Its inner layer is a huge ball of iron-nickel alloy (this isn't confirmed), and it's pretty much as hot as the sun at 5,500 degrees Celsius. The size of this metal ball is about 70% the size of the moon (760 miles in radius). The outer core is iron and nickel liquid and it's 1,600 miles thick. The temperature is even hotter than the inner core at 5,200 degrees Celsius.
The workings of the Earth's core is what creates our magnetic field. In the center of the Earth the field is about 50 times more powerful. Without the outer core, life on Earth would be very different. This magnetic field extends outward from the Earth for several thousand miles and creates a protective magnetosphere around the Earth that deflects the Sun's solar wind. Without this field, the solar wind would directly strike the Earth's atmosphere and render our planet lifeless. If there wasn't already enough to worry about. :)