What implication does the preservation of large, chemically isolated bodies like the African and Pacific anomalies suggest about the Earth's deep interior over geological time?

That mantle flow dynamics might be more stratified or slower in certain deep regions

The continued existence of such large, chemically distinct structures spanning billions of years directly challenges standard models of mantle convection that often predict homogenization over such vast timescales. If the deep mantle were constantly churning with enough intensity, these massive fragments of Theia should have eventually mixed entirely with the surrounding Earth-derived material. The fact that these anomalies persist relatively intact suggests that the convective forces driving mantle motion in these deep, stable regions—specifically beneath Africa and the Pacific—are either stratified, allowing the denser material to remain segregated, or significantly slower than expected, permitting these ancient seeds to resist dissolution across eons.