The world’s oceans have two main areas: the shallow continental shelf and the deep, dark abyssal plain. The continental shelf is home to most of the world’s marine life, while the abyssal plain is largely devoid of life, with only a few species able to survive in the extreme conditions. During ice ages, sea levels drop and continental shelves are exposed. Famous continental shelf areas include the Siberian Shelf, Sunda Shelf, North Sea Shelf, and Persian Gulf Shelf.
In the world’s oceans, there are two distinct geographic areas: the continental shelf and the deep ocean, also known as the abyssal plain. The continental shelf is a large area of shallow sea (less than 150m, 500ft) extending approximately 50 miles (82km) from the world’s continents. During ice ages, more water is locked up in the world’s ice sheets, sea levels drop, and continental shelves are exposed. Famous continental shelf areas include the Siberian Shelf, which humans once traversed in the Americas, the Sunda Shelf in the South China Sea, the North Sea Shelf, and the Persian Gulf Shelf, all of which are thought to have been inhabited by humans. .
Outside the continental shelf, continental crust gives way to oceanic crust, usually a different tectonic plate. Depth increases, with the bottom sloping at an angle between 1° and 10°. Below a depth of about 0.9 km (3,000 feet), sunlight can no longer reach the depths of the ocean and the pressure is about 90 times greater than at the surface, equivalent to the pressure on the surface of Venus. Only a few animals can survive deeper than this, as ecosystems must depend on debris falling from above or on chemotrophic bacteria that feed on hydrothermal vents or cold seeps at the bottom. In the completely dark environment, many animals are able to generate their own light, an ability known as bioluminescence.
Most of the world’s marine life is found on the continental shelf, where it is well lit. This marine life includes representatives of 37 of all 38 animal phyla: only one phylum, the velvet worms, lacks a marine version. Corals and sponges create a colorful seabed and thousands of fish species dodge predators among the kelp forests. Outside the continental shelf, there is also life, but most of it is within 150 m (500 ft) of the surface.
The dark abyssal plains that cover most of the ocean floor are largely deserts, devoid of life. Some species that live here include nematodes, giant isopods, and exotic primitive fish like blobfish.
Protect your devices with Threat Protection by NordVPN
