The layer of the Earth that contains partially molten rock and very high temperatures is the mantle.

Here's a breakdown:

* Crust: The outermost layer, relatively thin and solid.

* Mantle: The thickest layer, made up of mostly solid rock but with a partially molten layer called the asthenosphere. The asthenosphere is where convection currents occur, driving plate tectonics.

* Outer Core: Liquid iron and nickel.

* Inner Core: Solid iron and nickel, despite extreme temperatures due to immense pressure.