The activation of semi-core electrons might be crucial also for the phase transitions of other systems. MgO, for example, is observed to transform from B1 to B2 at exceptionally high pressure, ~ 400 -600 GPa. On the other hand, CaO undergoes the same phase transition at ~ 60 GPa, and SrO at only ~30 GPa. BaO does not turn into a B2 phase, but prefers an hexagonal NiAs phase between 10 -15 GPa, followed by a tetragonal PH4I phase. Also in these systems, we can notice a tremendous jump in the phase transition vs pressure trend. Therefore, the activation of the semi-core electrons might be relevant also for the phase transitions of the heavier earth alkaline metals. This possibility, particularly interesting for its geochemistry implications, will be examined in future works.