Which layer of the Earth is primarily made up of molten rock?

The outer mantle of the Earth is primarily made up of molten rock, also referred to as magma. This layer exists beneath the Earth's crust and is semi-fluid, allowing for the movement of tectonic plates and playing a crucial role in volcanic activity. The molten rock in the outer mantle is generated by intense heat and pressure from the Earth's core, leading to the formation of magma that can rise to the surface during volcanic eruptions.

In contrast, the crust is the solid outermost layer of the Earth, while the core consists mainly of solid iron and nickel in the inner part and a liquid outer layer. The inner mantle, while it does contain some molten rock, primarily consists of solid silicate minerals and is under immense pressure, which keeps it mostly in a solid state, unlike the outer mantle which allows for the presence of liquid magma.