Plate tectonics and the ocean floor
The shape of the ocean floor, its bathymetry, is largely a result of a process called plate tectonics. The outer rocky layer of the Earth includes about a dozen large sections called tectonic plates that are arranged like a spherical jig-saw puzzle floating on top of the Earth's hot flowing mantle. Convection currents in the molten mantle cause the plates to slowly move about the Earth a few centimeters each year. Many ocean floor features are a result of the interactions that occur at the edges of these plates.

The shifting plates may collide (converge), move away (diverge) or slide past (transform) each other. As plates converge, one plate may dive under the other causing earthquakes, forming volcanoes, or creating deep ocean trenches such as the Mariana Trench. Where plates are pulled away (diverge) from each other molten magma flows upward between the plates forming mid-ocean ridges, underwater volcanoes, hydrothermal vents, and new ocean floor crust. The Mid-Atlantic Ridge, is an example of this type of plate boundary. Transform boundaries are formed when two plates slide past one another such as on mid-ocean ridges and often cause earthquakes due to zig-zag offsets.