LITHOSPHERE


The Lithosphere is the rigid outer layer of the Earth, which includes the crust and the uppermost part of the mantle. Oceanic lithosphere is lithosphere with oceanic crust. Continental lithosphere is lithosphere with continental crust. Plates are made of lithosphere and are also refered to as lithospheric plates.

The Crust is the upper seismic layer of the Earth.. Also, ocean crust is made of denser minerals than continental crust.The crust has a relatively low density and low seismic wave speeds. It is about 7 km thick under oceans (oceanic crust), and 20-80km thick (averaging 35km), can be up to 65 km thick, under continents (continental crust). Oceanic crust is composed mainly of rocks with composition similar to basalt; continental crust mainly of rocks with compositions similar to granite.

The Asthenosphre (also know as the ductile mantle). The asthenosphere is solid even though it is at very hot temperatures of about 1600 C due to the high pressures from above. However, at this temperature,  minerals are almost ready to melt and they become ductile and can be pushed and deformed like silly putty in response to the warmth of the Earth. These rocks actually flow, moving in response to the stresses placed upon them by the churning motions of the deep interior of the Earth. The flowing asthenosphere carries the lithospheric plates of the Earth, including the continents, on its back.

Relative position of the different layers of the Earth: Contrast between Lithosphere and Asthenosphere. Images from USGS <http://pubs.usgs.gov/gip/dynamic/inside.html>

More information on the Crust and Lithosphere