Abyssal plains occupy most of the ocean floors: where pitch black reigns over high pressure and minimal sedimentation, which chiefly consists of fine clay particles and marine snow: the organic detritus of oceanic microorganisms.
Mid-ocean ridges are long, linear, oceanic mountain chains. These regions are subject to intense geological activity from tectonic plates moving apart (divergent boundaries). In contrast, trenches are deep troughs, typically at the margins of continents, where a crustal slab is subducted into the mantle.
At every depth, the sea floor has varied terrain and geological features, such as seamounts and reefs, as well as trenches and other seabed carvings. The same forces that shape terra firma work in the dark on the ocean floor; only water does all the work there, whereas wind lays its hand on the land.