LITHOSPHERE.

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Posted by: Global Warming in CAUSES June 6, 2013 1 Comment 1 Views

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Lithosphere

 

Lithosphere besides compositional classification, the Earth is separated into layers based on mechanical properties. The topmost layer is called the lithosphere, composed of tectonic plates that float on top of another layer known as the asthenosphere. The term lithosphere is derived from the Greek words lithos, meaning rock, and sfaira, or sphere. The rigid, brittle lithosphere extends about 70 kilometers and is made up of Earth’s crust and the upper part of the mantle underneath. It is broken into a mosaic of rigid plates that move parallel across the Earth’s surface relative to each other lithosphere.

 

The lithosphere rests on a relatively ductile, partially molten layer known as the asthenosphere, which derives its name from the Greek word asthenes, meaning “without strength.” The asthenosphere extends to a depth of about 400 kilometers in the mantle, over which the lithospheric plates slide along. Slow convection currents within the mantle, generated by radioactive decay of minerals, are the fundamental heat energy source that causes the lateral movements of the plates on top of the asthenosphere. According to the plate tectonic theory, there are approximately twenty lithospheric plates, each composed of a layer of continental crust or oceanic crust.

Lithosphere

These plates are separated by three types of plate boundaries. At divergent boundaries, tensional forces dominate the interaction between the lithospheric plates, and they move apart and new crust is created. At convergent boundaries, compression of lithospheric plate material dominates, and the plates move toward each other where crust is either destroyed by subduction or uplifted to form mountain chains. Lateral movements due to shearing forces between two lithospheric plates create transform fault boundaries. The lithosphere earthquakes and volcanic activities are mostly the result of lithosphere plate movement and are concentrated at the plate boundaries.

 

The lithosphere´s plates move at a rate of about 3 centimeters per year. The distribution and relative movement of the oceanic and continental plates across the latitude also have profoundly affected the global climate. The major contributing factors are differences in surface albedo, land area at high latitudes, the transfer of latent heat, restrictions on ocean currents, and the thermal inertia of continents and oceans. Lithosphere according to the present configuration of oceans and continents, the lithosphere low latitudes have a greater influence on surface albedo because the lower latitudes receive a greater amount of solar radiation than the higher latitudes.

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