Here's why:

* Outer Core: This layer is composed primarily of liquid iron and nickel. The immense pressure from the layers above keeps the outer core from solidifying, even though the temperature is incredibly hot.

* Inner Core: While incredibly hot, the intense pressure of the entire planet forces the inner core into a solid state, even though it is made of the same materials as the outer core.

* Mantle: The mantle is mostly solid rock, but it behaves like a very viscous fluid over long periods. This is due to the extreme heat and pressure.

* Crust: The Earth's crust is the solid, outermost layer and is much cooler than the other layers.

Let me know if you have any other questions!