The oceanic trenches

* Table of oceanic trenches.

The planets are assumed to consist of successive layers of increasing density.
The materials are in order of their density, the iron center and the iron sulfide, silicates, water, nitrogen, carbon dioxide, ammonia, methane, helium, hydrogen . There is yet no two identical planets in their structures, each with its own characteristics.
The native iron first abundant condensate Solid grains of chemical and mineralogical birth fused in the nebulae, the following is called: the sequence of condensation. The first compounds that condense at 1300 ° C, are rich in titanium oxides, aluminum and calcium. To 1050 ° C condenses massive metallic iron and then to 950 ° C, the first case the silicate magnesium silicate and iron. To 800 ° C, to form silicates looser structures, feldspars and iron sulfide. At even lower temperatures condenses silicate containing water at 0 ° C and the water condenses into ice. is a constituent of the Earth's core.
Silicon, magnesium silicate and iron are essential components of Earth's mantle.
Feldspar, condensate gives the basalt, forms the floor of Earth's oceans.
The internal structure of the Earth is divided into several successive envelopes, the Earth's crust, mantle and core. This representation is very simplified since the envelopes can themselves be decomposed.
To identify these layers, seismologists use seismic waves, when the speed of a seismic wave suddenly changes, there is change of environment, so layer.
This method allowed, for example, determine the state of matter at great depths (deep mantle, core).
These layers are bounded by discontinuities such as the Moho between the crust and mantle, that of Gutenberg between the mantle and core.
The Earth formed by accretion of meteorites and the different layers are implemented in accordance with the density of its constituents.

The theory of plate tectonics is now recognized since the late 1960s and widely needed in the scientific world. In the 19th century it was hard to believe that entire continents could drift.
We know now that the solid mantle is driven by huge convection currents that flow over millions of years.
The image we have now is a complex and active planet whose crust is composed of oceanic and continental plates of different mineral compositions, constantly moving under the combined action of convection currents and internal gravity land.
Continental blocks formed by collision of continental plates and tear, according to a cycle of 400 million years.
Oceanic plates are heavier, are participating in this ballet constant for several billion years and often end up diving in the Earth's interior by subduction, thus helping to recycle the Earth's crust whose thickness varies between a few kilometers and 65 km.
The seed (inner core) is a solid ball of 1220 km radius, located at the center of the Earth.
Seismologists suspect the existence of an almond in it. It is surrounded by the liquid core composed of an alloy of molten iron.
The seed increases, by crystallization of liquid iron core, which cools slowly.

* The structure of the Earth: the continental crust on the surface has a thickness of 30 to 65 km, upper mantle with a thickness of 670 km, the lower mantle with a thickness of 2180 km, the outer core with a thickness of 2270 km, the inner core of a thickness of 1220 km.

nota : The topography can be measured and then represented on a map the shapes and details visible from Earth. Bathymetry is the science of measuring ocean depths to determine the topography of the seafloor.

* Bathymetry and topography of the land and oceans to -12,000 + 9000 meters (satellite data). Ifremer source.