Earth's layers vary vastly in terms of temperature, the core being the hottest, and the crust being the coolest. This is the result of the immense pressure, literally the weight of the world, that is forced towards Earth's core by gravity.
The size of these layers varies greatly as well. The crust, in comparison to all other layers, is extremely thin, making up only around 15% of Earth, while the mantle makes up around 84% for comparison.
