Here's a breakdown:

* Crust: This is the outermost layer, and it's very thin compared to the other layers. It ranges from about 3-5 miles thick under the oceans (oceanic crust) to 25 miles thick under the continents (continental crust).

* Mantle: This is the thickest layer, extending about 1,800 miles down.

* Outer Core: This is a liquid layer of iron and nickel, about 1,400 miles thick.

* Inner Core: This is a solid ball of iron and nickel, about 750 miles thick.

So, while the crust is incredibly thin compared to the entire Earth's diameter, it's still an essential layer for life on Earth and its geological processes.