Beyond the continental rise exist the deep ocean basins. Large, smooth plains (abyssal plains) are located on the ocean floor. These plains are the flattest parts of the ocean floor. The ocean floor is basalt rock, but the abyssal plains can be covered with hundreds of kilometers of fine-grain sediments, deposited on top of the basalt after hundreds or thousands of years of erosional processes that carried sediments from land to the continental margins, and eventually to the abyssal plains.

Deep sea trenches are also located on the ocean floor. Deep sea trenches are the deepest areas in the ocean. The largest deep sea trench is the Marianas Trench, located in the Pacific Ocean near Japan . It is not only the deepest part of the ocean - it is also the deepest place on Earth! Many deep sea trenches are located around the margins of the Pacific Ocean. Why would this be? Remember back to the unit on plate tectonics - what is located around the Pacific Ocean? Hopefully you remember that the Pacific Ocean is ringed by convergent plate boundaries . In addition to volcanoes and earthquakes, oceanic-oceanic and oceanic-continental convergence cause the formation of deep sea trenches when one ocean plate is subducted beneath another.

The mid-ocean ridges are also located on the ocean floor. Mid-ocean ridges are underwater mountain ranges that run along the floor of all the Earth's oceans. The world's tallest mountains are located here, as part of the mid-ocean ridge; many of them are taller than Mt. Everest!