No real geochemical indication of the existence of
primitive material
Strong indications that the 670 km depth boundary is
permeable
Strong indications of a viscosity increase with
depth by 10-100
This viscosity increase does not stratify the
mixing
3D convection
more efficient mixer with, than without plates
Highly viscous, small, primitive blobs may
survive(?)
Need of a reservoir to store incompatible
elements
Seems difficult to hide a dense reservoir in the
mantle
Crust segregation in D'' may be the deep enriched
reservoir
(EM, HIMU)
The remaining lithosphere may be the depleted
(''primitive-like'')
reservoir