Here's why:

* Inner Core: The inner core is incredibly hot, estimated to be around 5,200°C (9,392°F) due to immense pressure.

* Outer Core: While the outer core is still hot, it's liquid and less dense than the inner core. This means the pressure is lower, and the temperature is around 4,500°C (8,132°F). It's important to remember that this is still incredibly hot, but it's significantly cooler than the inner core.

* Mantle: The mantle is a thick layer of mostly solid rock, with temperatures ranging from around 1,000°C (1,832°F) at the top to 3,700°C (6,692°F) at the bottom.

* Crust: The crust is the outermost layer and is relatively cool compared to the other layers. Temperatures vary significantly depending on location, but generally range from 0°C (32°F) near the surface to around 1,100°C (2,012°F) at the base.

Therefore, even though the outer core is extremely hot, it is the coldest layer of the Earth when compared to the inner core, mantle, and crust.