Earth is divided into four layers: crust, mantle, outer core, and inner core. Each layer has unique properties.

The Earth's crust*** is like the skin of an apple or the shell of an egg. It is very thin in comparison to the other three layers. The crust is only about 8 kilometers (3 to 5 miles) thick under the oceans (oceanic crust***) and about 32 kilometers (25 miles) thick under the continents (continental crust***). The crust is composed of two types of rocks. The continental crust is mostly granite. The oceanic crust is mostly basalt. Basalt is much denser than the granite. Because of this the less dense (less tightly packed) continents ride on the denser (more tightly packed) oceanic plates. 

 

The mantle*** is the largest layer of the Earth at 2900 km thick (1800 miles). The middle mantle is composed of very hot packed rock that flows very slowly (kind of like the paste we made or like honey). Because the middle mantle flows like a half-liquid, half-solid, there is some movement that goes on here.

 

The core of the Earth is like a ball of very hot metals. The outer core*** is so hot that the metals in it are all in the liquid state. The outer core is composed of the melted metals of nickel and iron. Its thickness is estimated to be around 2259 km (1404 miles) 

 

The inner core*** of the Earth is about 1200 km (760 miles) thick and has temperatures and pressures so great that the iron and nickel metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place like a solid. 

 

 If it were possible for you to dig a hole to the center of the Earth, you would find as you moved from the crust to the mantle that the temperature increases the lower you go, with the core being even hotter than the surface of the sun. As it turns out, this temperature difference plays an important role in earthquakes, volcanoes, islands, and why the Earth even looks the way it does!