Low Q zone at the base of the mantle: Evidence for lower mantle convection?

Temperatures in the lower mantle of the Earth are estimated from the observed Q distribution. A thermal boundary-layer where temperatures rise rapidly is found at the base of the mantle, corresponding to the low Q zone described by Anderson and Hart (1978a,b). The existence of this thermal boundary layer indicates that the lower mantle participates in convection, and also that some of the energy driving the convection is coming from the core.