Plate tectonics is the theory that scientists use to explain the movement in the Earth's crust. Similar to a model, a theory explains a chain of evidence. However, a theory cannot be directly tested. Since this cannot be done, plate tectonics remains as an accepted theory subject to revision as new evidence is gathered. Scientists believe that there are seven large plates and thirteen smaller plates that cover the surface of the Earth.
Some scientists argue that the numbers of plates are different.
A plate measure about 100 km in thickness. Plate tectonics states that the Earth's plates are constantly moving. These movements, even though they are very small, cause changes in the crust of the Earth. The Theory of Continental Drift explains the movements of the plates. The continents are attached to the plates.