Here's a breakdown:

* Crust: The thin, outermost layer, like the skin of an apple.

* Mantle: The thickest layer, composed mostly of solid rock, but with a semi-molten layer called the asthenosphere. It makes up about 84% of Earth's volume.

* Outer Core: A liquid layer of iron and nickel.

* Inner Core: A solid ball of iron and nickel, under immense pressure.

So while the inner core is the densest, the mantle is the largest in volume.