Many forces cause the surface of the Earth to change over time. However, the largest force that changes our planet’s surface is the movement of Earth’s outer layer through the process of plate tectonics. This process causes mountains to push higher and oceans to grow wider.
As shown in this diagram, the rigid outer layer of the Earth, called the lithosphere, is made of plates which fit together like a jigsaw puzzle. These plates are made of rock, but the rock is, in general, lightweight compared with the denser, fluid layer underneath. This allows the plates to “float” on top of the denser material.
Movements deep within the Earth, which carry heat from the hot interior to the cooler surface, cause the plates to move very slowly on the surface, about 2 inches per year. There are several different hypotheses to explain exactly how these motions allow plates to move.
Interesting things happen at the edges of plates. Subduction zones form when plates crash into each other, spreading ridges form when plates pull away from each other, and large faults form when plates slide past each other.A map of Earth’s tectonic plates. Plate boundaries are shown in red. Learn more about the geologic features related to Earth’s tectonic plates at This Dynamic Planet.
Click on image for full size
Modified from USGS source : windows to the universe