Denis Diderot

See also: Oceanography

The Océanographie is science studying the seas and oceans; it truly began with great explorations from 18th and 19th centuries. With crossed multiple fields, one usually divides it into four large branches: the geology marinades which studies sea-beds, the physical oceanography which studies the physical characteristics (vague, tides, currents…), the chemical oceanography which deal with the composition of water and its interaction with the atmosphere, and the marine biology which studies the life of the oceans. Sometimes one adds to these disciplines marine meteorology and maritime engineering. These various aspects of the oceans are described below.

Marine geology

The Géologie marinades described the structure of the ocean floor: geologically, an ocean is an ocean floor covered by water. The floor or oceanic crust is distinguished from the continental crust, by:

1. its composition: the ocean floor is the fine layer of solidified volcanic Basalte which recovers the coat where there are no continents. The oceanic crust has as a Lithologie basic as the continental crust.
2. its thickness: 5 to 7 km on average, against 30 km on average for the continental crust;
3. a more important Density from 3,24 to 3,27, against 2,7 to 2,8 for the continental crust.

The oceanic crust is also youngest, since it is formed by the épanchements dorsal Lave at the top of the S oceanic. Thus, the oldest rocks found coming from the continental crust go back to 3700 million years, while oldest coming from the oceanic crust go back to 220 million years. The transition between crusts oceanic and continental is carried out on the level of the continental shelf, either in a gradual way (Marge passivates), or in a more brutal way with an active margin or zone of Subduction.

The underwater geomorphology distinguishes the great characteristics from the funds. Close to the coasts, one finds the continental shelf, of slope very weak and going down up to 130 - 150 Mr. the more accentuated slope (4 with 5° on average, locally stronger) which succeeds to him is the continental Slope which goes down until 2  000 - 3  000 meters, with its foot the continental Glacis where the Sédiment S. These units accumulate form the Continental terrace or précontinent and crossed by long the underwater pits sometimes very deep, and the dorsal , similar to the assembly lines on ground. In the middle of the dorsals, the major Rift (1500 to 1800 m) is the place where the new crust is created by épanchement Lave. Underwater volcanicity gives also other landscapes like the underwater mounts and the underwater volcanos, becoming volcanic islands when they emergent.

Physical oceanography

Chemical oceanography

Marine meteorology

Marine biology

The ocean and human being

Exploration

If the way on surface the oceans is practiced of long time, the exploration of sea-beds was not possible that recently.

The major point of the oceans is the Challenger abyssal zone of the Fosse of Mariannes, located in the Pacific Ocean close to the the Northern Marianna Islands of North. Completely explored in 1951 by the British ship Challenger II , his maximum depth reaches 10.923 Mr.

The majority of the ocean floor are unexplored and is not charted. A total chart of sea-beds with a resolution of 10 km, created in 1995 on the basis of gravitational anomaly of oceanic surface, is in constant improvement, thanks to the accumulation of altimetric measurements which one calculates an average.

Natural resources

Pollution

Mythology

Other oceans

Disappeared oceans

The Plate tectonics having reconfigured the aspect of the Earth, there existed several oceans in the past, from now on disappeared (this list is not exhaustive):

• Panthalassa, the vast ocean surrounding the Supercontinent of the Pangée;
• Téthys, located between the Gondwana and the Laurasie;
• Tornquist, the southernmost ocean between Baltica and Avalonia.
• the Ocean Centralien, ocean of the Dévonien.
• the Ocean Rhéique, ocean of the Silurien and Dévonien.
• the Ocean Iapetus, ocean of the Cambrien and the Silurien.

Extraterrestrial oceans

The Earth is the only known astronomical object presenting liquid water to its surface and is probably only Solar system. However, of liquid water exists under the surface of several satellites, like Europe or probably Callisto and Ganymède. It is possible that other satellites (Triton inter alia) have internal oceans from now on cold. The planets Uranus and Neptune could not have liquid water oceans in lower part of their atmosphere, because they are gas balls whose core would be solid. The chemical composition of these cores is cold hydrogen. However the scientists try to look further into research on these planets.

The existence of an old ocean on the northern hemisphere of Mars is currently prone to debate, as what it would be occurred by it. Recent discoveries carried out by the mission " Mars Exploration Rover " indicate that Mars had water in at least a place.

One thinks that Titan has liquid hydrocarbons on its surface, more probably in the shape of lakes than of oceans.

Appendices

General references

• See the sources of the detailed Articles of each section.