Explain what tectonic plates are and what controls their movements.

A tectonic plate is a piece of Earth’s crust. There are about 15 of them on earth. Their movement sometimes brings earthquakes or volcanoes. That’s why most earthquakes are located on the border of two plates. They move a few centimeters a year, because the inner layer of the earth, consisting of soft “liquid” rocks, are moving because the difference in temperature between the earth's core and the earth's surface.