Structure of the earth

When studying plate-tectonics the best starting point is examining the structure of the earth. The earth is very similar to a peach in its structure. In the centre is a solid core. Surrounding the core is the inner core, then the mantle, which is covered in the earths 'skin' or crust.

Continental Drift and Plate Tectonics

In 1912 Alfred Wegener published a theory to explain why the Earth looked like a huge jigsaw. He believed the continents were once joined forming a supercontinent he called Pangaea. Over 180 million years ago this supercontinent began to "break up" due to continental drift.
During the 20th Century, scientists developed the theory of Plate Tectonics. The theory suggested that the crust of the Earth is split up into seven large plates (see map below) and a few smaller ones, all of which are able to slowly move around on the Earth's surface. They float on the semi-molten mantle rocks, and are moved around by convection currents within the very hot rocks.
The are two types of tectonic plates - continental plates and oceanic plates.

Plate Boundaries

  The point where two or more plates meet is known as a plate boundary. There are four main types of plate boundary. These are constructive, destructive, conservative and collision margins.

Plate Boundary	Diagram	Description	Example
Tensional / Constructive (divergent ) plate boundaries		Constructive plate boundaries occur when two plates move away from each other.	North American and Eurasian Plate
Compressional / Destructive (subduction zones) plate boundaries		Destructive plate boundaries occur when an oceanic plate is forced under (or subducts) a continental plate.	Pacific Plate and the Eurasian Plate
Conservative (transform faults) plate boundaries		Conservative plate boundaries occur when two plates slide past each other.	North American Plate and the Pacific Plate
Collision plate boundaries		Collision plate boundaries occur when two continental plates move towards each other.	Indo-Australian and the Eurasian Plate