Renaming D double prime



“Knowledge about the dynamics of the D double prime region is a key to unlocking some fundamental mysteries of the Earth's heat engine which governs a wide range of global geophysical processes from tectonics to the geodynamo.”

This benign sentence makes complete sense to many geophysicists. But for many others, it all makes sense except for the odd nomenclature “D double prime.” One knows about the crust, upper and lower mantle, outer and inner cores, but where is the D double prime region? What meaning does it convey? Where is the D prime region, or the D region, or the A, B, and C regions for that matter, and are there higher-order primes? How did such an odd name come about anyway?