1. Upper Mantle: This layer extends from the base of the crust (Moho discontinuity) down to a depth of about 660 km (410 miles). It is further subdivided into the lithosphere (rigid, outermost part) and the asthenosphere (semi-molten, weaker layer).
2. Lower Mantle: This layer extends from the base of the upper mantle to the outer core, at a depth of about 2,900 km (1,800 miles). It is characterized by higher pressures and temperatures than the upper mantle.
While there isn't a third distinct sublayer, the transition zone within the upper mantle (from 410 to 660 km) is sometimes considered a separate layer due to the presence of different mineral phases and a change in seismic wave velocities. However, it is not typically considered a distinct sublayer like the upper and lower mantle.
