Here's a breakdown:

* Crust: The outermost layer of Earth, made of solid rock.

* Mantle: The thickest layer, mostly solid rock but with a partially molten layer called the asthenosphere.

* Outer Core: Liquid iron and nickel.

* Inner Core: Solid iron and nickel due to immense pressure.

The asthenosphere is the source of magma. It's a partially molten layer within the mantle where the rock is hot enough to partially melt. This molten rock, called magma, can rise through the crust and erupt as lava during volcanic eruptions.