Continental crust: a layer of rock (~30km thick) having the composition of granite that constitutes the continents. Mantle: the middle (and thickest) layer of the solid earth, lying beneath the crust, and above the core, composed of silicate materials. Lithosphere: outer rigid shell of earth (including upper mantle, and ocean/continental crust) characterized by being strong and rock-like, divided into plate that move as rigid units during tectonic processes. Asthenosphere: a partially molten layer of rock in the upper mantle that is weak enough to flow and cause movement of the overlying lithospheric plate. Plate tectonics: tectonic interactions resulting from the movement of lithospheric plates. Tectonic plates: divisions of the upper solid earth (lithosphere) move as rigid plates in tectonic processes. Convergent margins: a boundary between two lithospheric plates that move towards each other and cause a collision of continents or subduction of one plate beneath the other. Transform fault margin: a boundary between lithospheric plates where the plates slide.