The Mantle

The mantle is the vast layer of the Earth's interior that lies just beyond the crust. It begins at the Moho discontinuity and continues down to a depth of 2,900 km. Everything below the crust, right up to the core, belongs to this layer.

The upper portion of the mantle is called the asthenosphere. The word astheno means weak, which tells you something important about this layer's nature. It is considered to extend up to about 400 km in depth. This is the main source of magma — the molten rock that finds its way to the surface during volcanic eruptions. Because it is weak and partially molten, it allows the rigid plates above it to move.

The crust and the uppermost part of the mantle together form the lithosphere. Its thickness ranges from 10 to 200 km. This is the solid, rigid shell that makes up the tectonic plates.

Below the asthenosphere lies the lower mantle, which extends beyond it. Unlike the asthenosphere, the lower mantle is in a solid state. …