Which option is not an example of chemical classification?

Correct answer: Asthenosphere

The direct answer is D, Asthenosphere. Chemical classification divides Earth according to what materials the layers are made of. By this system, the broad layers are crust, mantle and core. The crust is the outer rocky layer, the mantle is the thick layer below it, and the core is mainly metallic, especially iron and nickel. Asthenosphere is different: it is identified mainly by its physical or mechanical behaviour. It is a weak, hot, partly plastic zone in the upper mantle on which tectonic plates can move. Option A, Crust, is correct as a chemical layer. Option B, Mantle, is also a chemical layer. Option C, Core, is also a chemical layer. Option D, Asthenosphere, is not a chemical division; it belongs to the mechanical or physical classification of Earth’s interior. Do not confuse the material-based names crust, mantle and core with behaviour-based names such as lithosphere, asthenosphere, mesosphere, outer core and inner core. Memory cue: “chemical means composition; mechanical means behaviour.”