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The asthenosphere (from Ancient Greek ἀσθενός (asthenós) 'without strength') is the mechanically weak [1] and ductile region of the upper mantle of Earth. It lies below the lithosphere , at a depth between c. 80 and 200 km (50 and 120 mi) below the surface, and extends as deep as 700 km (430 mi).
The lithosphere–asthenosphere boundary lies between Earth's cooler, rigid lithosphere and the warmer, ductile asthenosphere. The actual depth of the boundary is still a topic of debate and study, although it is known to vary according to the environment. [1]
Below the asthenosphere, the mantle is again relatively rigid. The Earth's mantle is divided into three major layers defined by sudden changes in seismic velocity: [6] the upper mantle (starting at the Moho, or base of the crust around 7 to 35 km [4.3 to 21.7 mi] downward to 410 km [250 mi]) [7]
Earth's crust ranges from 5 to 70 kilometres (3.1–43.5 mi) [7] in depth and is the outermost layer. [8] The thin parts are the oceanic crust, which underlies the ocean basins (5–10 km) and is mafic-rich [9] (dense iron-magnesium silicate mineral or igneous rock). [10]
Earth systems across mountain belts include the asthenosphere (ductile region of the upper mantle), lithosphere (crust and uppermost upper mantle), surface, atmosphere, hydrosphere, cryosphere, and biosphere. Across mountain belts these Earth systems each have their own processes which interact within the system they belong.
Observations of rocks exposed on the surface and other evidence reveal that the upper mantle is mafic minerals olivine and pyroxene, and it has a density of about 3.33 g/cm 3 (0.120 lb/cu in) [1] Upper mantle material that has come up onto the surface comprises about 55% olivine and 35% pyroxene, and 5 to 10% of calcium oxide and aluminum oxide ...
[2] [3] Mantle convection causes tectonic plates to move around the Earth's surface. [4] The Earth's lithosphere rides atop the asthenosphere, and the two form the components of the upper mantle. The lithosphere is divided into tectonic plates that are continuously being created or consumed at plate boundaries.
Only beneath mid-ocean ridges does it define the lithosphere–asthenosphere boundary (the depth at which the mantle becomes significantly ductile). The Mohorovičić discontinuity is 5 to 10 kilometres (3–6 mi) below the ocean floor , and 20 to 90 kilometres (10–60 mi) beneath typical continental crusts, with an average of 35 kilometres ...