Earth and Space

Crust - the thin outer layer we see. It is made of cool, solid rock. It can either be oceanic crust or continental crust.

Mantle - a rock that behaves similarly to modeling clay. It can move, but only very slowly. Temperatures range from 500°C to over 4,000°C (932°F to over 7,232°F).

Outer core - very hot liquid iron and nickel. Temperatures range from 4,400°C to 6,100°C (7,952°F to 11,012°F).

Inner core - solid, composed mostly of iron and some nickel. Even though it is very, very hot, the weight of all the rock above it causes the inner core to remain in a solid state.

Heat Transfer - is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. 

Conduction- the process by which heat or electricity is directly transmitted through a substance when there is a difference of temperature or of electrical potential between adjoining regions, without movement of the material.

Convection - the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.

Radiation - the emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles which cause ionization.

Why are there oceans? Oceanic crust is made of basalt while continental crust is made of granite. The denser oceanic crust sits lower and sinks deeper into the mantle than continental crust, causing depressions that fill with water to create oceans.

Why is the core so hot? The process of nuclear fission, the splitting of atomic nuclei of elements such as uranium, occurs in the core. This process releases heat. Then, it takes a long time for that heat to move via conduction through the inner core and via convection currents through the outer core and mantle.