What is true about convection in Earth's mantle and tectonic plate motion?

Answer 1

Within the earth's mantle, which is semi-molten, there are convection currents caused by differences in temperature. These currents apply force from beneath to the plates of the earth's crust. The plates move slightly, which causes the very slow change in the shapes of our continents and oceans (and also causes occasional earthquakes).

All of this is true about convection currents, however there is significant dispute as to whether the tectonic plates are actually moved by convection currents. It could equally be true that "There are no convection currents in the Earth's mantle". Although is is the best theory going, there has been insufficient evidence that these currents actually exist. Alternative theories include:

• Continental drag: As a plate is subducted beneath another, the weight of the sinking end pulls the rest of the plate with it. This causes continental drift. The biggest flaw is that not all plates even have destructive boundaries.
• Hotspots: Hotspots themselves are responsible for continental drift (a similar sort of idea to convection currents, but we do know that hotspots exist). The biggest flaw is that not all plates have a hotspot on them.