What would be the significant geological differences on a planet that had no tectonic activity?
The answer to this question is rather complicated and depends on the size of the planet and the reason for the lack of tectonic activity. To see how this works, we need only look at the planetary bodies of our solar system. Of all the planetary bodies, only Earth seems to have developed full-fledged plate tectonics. In the case of most of the planets, this is because they were too small. (I am not considering the gas giants in this explanation because they are completely different from the planets with solid surfaces.) Because of their small sizes, they cooled too quickly for tectonics to develop. However, this does not mean that they have completely smooth surfaces. The lack of significant atmospheres on those bodies that are smaller than Mars means that they have nothing to protect them from meteorite impact and nothing much to erase impact craters. The result in the case of the Moon and Mercury is that we have too different surfaces. There are highly cratered highlands that represen
