Most of the oceans have a common structure, created by common
physical phenomena, mainly from tectonic movement, and sediment from
various sources. The structure of the oceans, starting with the
continents, begins usually with a continental shelf, continues to the continental slope – which is a steep descent into the ocean, until reaching the abyssal plain – a topographic plain,
the beginning of the seabed, and its main area. The border between the
continental slope and the abyssal plain usually has a more gradual
descent, and is called the continental rise, which is caused by sediment cascading down the continental slope.
The mid-ocean ridge, as its name implies, is a mountainous rise through the middle of all the oceans, between the continents. Typically a rift runs along the edge of this ridge. Along tectonic plate edges there are typically oceanic trenches – deep valleys, created by the mantle circulation movement from the mid-ocean mountain ridge to the oceanic trench.
volcanic island ridges are created by volcanic activity, erupting
periodically, as the tectonic plates pass over a hotspot. In areas with
volcanic activity and in the oceanic trenches there are hydrothermal vents – releasing high pressure and extremely hot water and chemicals into the typically freezing water around it.
Deep ocean water is divided into layers or zones, each with typical
features of salinity, pressure, temperature and marine life, according
to their depth. Lying along the top of the abyssal plain is the abyssal zone, whose lower boundary lies at about 6,000 m (20,000 ft). The hadal zone – which includes the oceanic trenches, lies between 6,000–11,000 metres (20,000–36,000 ft) and is the deepest oceanic zone.