(dee double-prime) layer.
To explain the observed convective regime in this structure, the Adams-Williamson equation is modified to include a tau-alpha corrective term that models a superadiabatic thermal gradient between it and the structure below it. The boundary between it and the region below it is home to ultra-low velocity zones and sees a remarkable drop off in S-wave activity, while radioactive decay and accretion heat lead to upwellings in this region whose lower bound is the D'' (dee double-prime) layer. Convection currents in this layer of the earth cause its namesake plumes and its fluidity is the reason for plate tectonics. For 10 points, name this largest layer of the earth that sits below the crust.
To explain the observed convective regime in this structure, the Adams-Williamson equation is modified to include a tau-alpha corrective term that models a superadiabatic thermal gradient between it and the structure below it.
mantle [accept core-mantle boundary for the first sentence]