When studied closely, we find that the Earth has a layered structure. It is made up of three main layers: the crust, the mantle and the core. The crust is the outermost part, the mantle is the middle layer and the core is the centremost layer. As we travel towards the core of the Earth, the temperature increases. On an average, the temperature increases about 1ºF (1ºF = –17.2ºC) for every 60 feet distance downwards. The rocks present beneath the surface of the Earth are very hot due to high pressure.