What is gravity's role in plate tectonics?

It creates a gradient of pressure increasing with depth and thereby enables convection in both the outer core (runny liquid metal) and mantle (semi-solid rock—solid enough to transmit S-type seismic waves but soft enough to ooze under great pressure). read more

However, plate tectonics are very superficial and mostly have to do with compression and tension on plates, and they are run by subduction and convection, which themselves are controlled by density which is also temperature dependent. read more

The main driving force of plate tectonics is gravity. If a plate with oceanic lithosphere meets another plate, the dense oceanic lithosphere dives beneath the other plate and sinks into the mantle. This process is called subduction. The sinking oceanic lithosphere drags the rest of the tectonic plate and this is the main cause of plate motion. read more

It’s the mantle convection that drives plate tectonics, because the continents are dragged around by the tops of the convective cells. And the pressure gradient enables convection because it creates both buoyancy and the need for buoyancy. read more