The seven major plates of Earth's lithosphere are part of the lithosphere.

Here's why:

* Lithosphere: This is the rigid outermost layer of Earth, composed of the crust and the uppermost part of the mantle. It's broken into large, movable tectonic plates.

* Asthenosphere: This is the layer beneath the lithosphere, within the upper mantle. It's a semi-molten, viscous layer that allows the tectonic plates to move.

So, the lithosphere is the mechanical layer containing the seven major plates.