1. Lithosphere, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of up to thousands of years or more. The crust and upper mantle are distinguished on the basis of chemistry and mineralogy.
2. The asthenosphere is the highly viscous, mechanically weak, and ductile region of the upper mantle of Earth. the lower boundary of the asthenosphere within the mantle is not well defined.
3. The Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the solidified and uppermost layer of the mantle.
4. A trench is a type of excavation or depression in the ground that is generally deeper than it is wide, and narrow compared with its length.
