The oceanic lithosphere consists of the upper part of the Earth's crust that is submerged beneath the oceans. It is primarily made up of basalt, but can consist of other forms of sediment deposited by rivers or currents; the basalt feature exists due to the oceanic lithosphere's creation via divergent tectonic activity. The continental shelf is a portion of the crust that is of higher elevation than the rest of the ocean due to its connection to the less dense continental lithosphere. The continental slope, therefore, is the portion of the crust where the continental shelf decreases in elevation as it meets the denser oceanic lithosphere. Abyssal plains are portions of the lithosphere far from spreading centers - they consist of rocks older than those near rifting centers. Due to the coolness of the plate and their distance from rifting centers, abyssal plains are some of the lowest continuous portions of the lithosphere (cool rock is denser and thus sinks to a lower elevation). Since they are very much inactive, abyssal plains are coated with sediment and are very, very flat.
