Deep Sea Plain

Deep sea plains are the vast, flat expanses that make up the floor of the ocean basins. Think of them as the ocean's version of a level, open field — they are the flattest and smoothest regions on the entire planet. Where the continental margins end and the deep ocean truly begins, these plains stretch out as the dominant feature of the seafloor.

These plains are not at a uniform depth everywhere, but they all lie within a specific range. The water depth over them varies between 3,000 and 6,000 metres. This puts them well below the reach of sunlight and far from the turbulence of surface waves, which is exactly why they remain so remarkably flat and undisturbed.

The smoothness of the deep sea plain is largely a result of what covers it. The plains are blanketed with fine-grained sediments, primarily clay and silt. Over immense stretches of time, these tiny particles have settled out of the water column and drifted down from the continents, slowly building up a soft, even layer that fills in any minor irregularities in the underlying rock. Because the sediments are so fine and the deposition is so uniform, the surface stays exceptionally level. …