Venus and Earth are often described as planetary “twins”; however, the large-scale volcano-tectonic surface features on each body indicate a different interior state and suggest that somewhere in their evolutions, they diverged. Certain features that represent a surface manifestation of the mantle convection within Venus show a “plume-thermal dichotomy”: large-scale mantle upwellings (plumes) appear to coexist in both space and time with many more small-scale mantle upwellings (i.e., thermals). How can we explain this coexistence of multiple scales (~100 km vs ~1000 km) of mantle convection on Venus, and why do these smaller-scale convective features, called coronae, not appear on the surface of the Earth? This talk will discuss the role that mineral phase transitions may play in the mantle convective dynamics of present-day Venus. The talk will also discuss the role that changes in mineral phase transitions may play in the long-term thermal evolution of terrestrial planetary bodies like Earth and Venus.