The theory of plate tectonics states that the Earth’s solid outer crust, the lithosphere, is divided into some large and small plates that move over the asthenosphere. Oceanic and continental plates come together, spread apart, and interact at boundaries all over the planet.
A divergent boundary occurs when two tectonic plates move away from each other. When two plates come together, it is known as a convergent boundary. The impact of the two colliding plates buckles the edge of one or both plates up into a rugged mountain range, and sometimes bends the other down into a deep seafloor trench. Two plates sliding past each other forms a transform plate boundary.