Here's why:
* The crust is the outermost layer. It's relatively thin and composed of solid rock.
* The hottest layer is the inner core. It's a solid ball of iron and nickel with temperatures estimated to be around 5,200° Celsius (9,392° Fahrenheit).
* The mantle, which lies between the crust and the core, is also much hotter than the crust.
Think of it like an onion: the crust is the outer skin, the mantle is the fleshy part, and the core is the very center. The deeper you go, the hotter it gets!
