Plate Tectonic Theory is a theory in the field of geology which was developed to provide an explanation for the existence of evidence of large-scale movements performed by the Earth's lithosphere. This theory has been included and also replaced the Continental Drift Theory which first put forward in the first half of the 20th century and the concept of seafloor spreading developed in the 1960s.
The outer portion of Earth's interior is formed from two layers. At the top there is the lithosphere consists of crust and upper mantle of a rigid and dense. Under the layers of the lithosphere there is asthenosphere its shaped solid but can flow like a liquid with a very slow and the geological timescale is very long because the viscosity and shear strength (shear strength) is low. Deeper, the mantle below the asthenosphere to be more rigid nature again. The cause is not a cooler temperature, but high pressure.
Layers of the lithosphere is divided into tectonic plates (Tectonic plates). On earth, there are seven major plates and many plates are smaller. These lithospheric plates ride on the asthenosphere. They are moving relative to each other at plate boundaries, both divergent (away), convergent (collide), or transform (sideways). Earthquakes, volcanic activity, mountain formation, and formation of oceanic trenches are all generally occurs in areas along plate boundaries. The lateral movement of the plates is typically 50-100mm / year.