The inner core is solid, fourth layer and made out of iron and nickel. It's the one mostly in charge for the other layers. If the inner core stopped spinning, the outer core would lose its magnetic field, and this will be bad because of the sun's radiation wave. Including the other layers.
The outer core is the liquid, third layer. It's in charge of Earth's magnetic field.
The mantle is the second layer of earth, the original temperature can come up about to 1000+ or more, celsius.