The liquid core of Earth—and, minimally, the solid part as well—is also pulled ever so slightly backward and forward by the Moon’s tidal action. Its motion is tiny (much, much less than ocean tides) but over billions of years that kind of tidal activity is like squeezing a rubber ball in your hand over and over: the core heats up. That heat eventually diffuses through the planet, affecting processes like volcanism and plate tectonics.