Except ridges in the World Ocean many heights, or oceanic plateaus are known. The largest of them in the Atlantic Ocean - the Bermudas plateau. On its surface - a number of underwater mountains of a volcanic origin.
Sedimentation - one of the most important factors of a relyefoobrazovaniye at the ocean. It is known that more than 21 billion t of firm rainfall annually come to the World Ocean, to 2 billion t of volcanic products, about 5 billion t of the limy and siliceous remains of organisms.
The second - transitional - a zone was created on a joint of continental blocks and oceanic platforms. It consists of hollows of the suburban seas, chains of mainly volcanic islands in the form of arches and narrow linear hollows - deep-water trenches with which the deep breaks leaving under the continent coincide.
Though the origin of oceanic pools remains still secret, a picture of how they were filled with water and as oceans in the geological past of Earth appeared and disappeared, it is possible to imagine more or less precisely.
Average depth of the World Ocean - about 4 thousand m is only 0,0007 radiuses of the globe. On an ocean share, considering that density of its water is close to 1, and density of a solid body of Earth - about 5,5, only the small part of mass of our planet is necessary. But if to address to a geographical envelope of Earth - to a thin layer in some tens kilometers, its most part will be made by World Ocean. Therefore for geography it is the most important object of research.
Rains, for centuries overthrown on Earth surface, were the main source of water which filled oceanic hollows. The sea, thus, was the atmosphere child in turn representing gaseous allocations of ancient Earth. The part of water arrived from Earth subsoil.