I. Plate Tectonics
Plates are large pieces of land that hold whole continents and oceans on them. Plate tectonics is the study of these plate, how they were formed, and how they move. The surface of the Earth is divided into 12 main plates and several smaller ones. Some are moving apart and some are colliding. Some are even sliding next to each other. Plates are approximately 100 meters thick, and along with the crust this forms the layer of the Earth called the lithosphere. The lithosphere is made mostly of basalt and granite The plates move because the mantle right below the plates, called the asthenosphere is partially melted and therefore allows the plates to move slowly.

II. Diverging Plate Boundaries
In certain cases, the lithospheric plates are moving apart. This usually forms mid-ocean ridges. Mid-ocean ridges have deep valleys called rift valleys. An example is the mid-Atlantic ridge, in which the rift separates the North American Plate from the Eurasian Plate, and the South American Plate from the African Plate.

III. Sliding Boundaries
At some boundaries, the plates are sliding past each other. In California, the San Andreas Fault is an example of a plate boundary where plates slide next to each other. A fault is a break in the Earth's crust where there was movement.

IV. Converging boundaries
In many cases the plates will move toward each other. This is called a converging boundary. There are two types of converging boundaries. One is called a collision boundary. The other is called a subduction boundary. In a collision boundary, if both plates hold continents, the plates will collide and the lithosphere at the boundary will be pushed upward. The two parts