What are the relationships among the mantle, the crust, the asthenosphere, and the lithosphere?
Earth is divided into 3 layers: Crust, Mantle, and Core, distinguished primarily by chemcal composition. The crust is the outermost shell, and is the thinnest layer, the mantle is the thickest layer and lies inbetween the crust and core. The core is the center of the earth, made up of mostly iron, and consisting of a liquid outer core and solid inner core.
Earth is also classified into 2 larger layers, which encompass the other layers: the lithospher and asthenosphere. The lithosphere is made up of the Crust and uppermost part of the Mantle and is rigid and brittle. The tectonic plates are part of the lithosphere. The Asthenosphere is under the lithosphere and is made up of the rest of the Mantle and the Core. It is viscous (behaves similar to a liquid) and the lithosphere essentially "floats" on top of it.