A typical plate that moves across the Earth's surface is made up of lithosphere, which is the rigid outermost layer of the Earth. This lithosphere is comprised of two parts:

1. Crust: This is the outermost layer of the Earth and is relatively thin compared to the other layers. It is divided into two types:

* Oceanic crust: Dense, dark-colored basalt rock, typically about 5 km thick.

* Continental crust: Less dense, light-colored granite rock, typically about 35 km thick.

2. Uppermost mantle: This layer is composed of a rigid, solid rock called peridotite. It is denser than the crust and extends down to about 100 km.

These two layers (crust and uppermost mantle) together form the lithosphere. It is broken into large pieces called tectonic plates.

The lithosphere rests on a hotter, more fluid layer called the asthenosphere. The asthenosphere is a part of the upper mantle that behaves like a very viscous fluid, allowing the rigid lithospheric plates to move over it.

Here's a simple breakdown:

* Plate = Crust + Uppermost Mantle (Lithosphere)

* Plate moves on top of the Asthenosphere (part of the upper mantle)

Key Point: It's important to note that the movement of the plates is caused by convection currents within the Earth's mantle. These currents are driven by heat from the Earth's core, which creates a circular motion in the mantle, dragging the plates along with it.