What causes the movement of tectonic plates according to the theory of plate tectonics?

The movement of tectonic plates is primarily attributed to convection currents within the Earth's mantle, which is a key concept in the theory of plate tectonics. As heat from the Earth's core warms the mantle, the heated material becomes less dense and rises toward the surface. When it reaches the cooler upper mantle and lithosphere, it loses heat and becomes denser, causing it to sink. This continuous cycle of rising and sinking creates convection currents that drive the movement of the tectonic plates situated above the mantle.

These currents can lead to the gradual movement of plates in various directions, causing earthquakes, volcanic activity, and the formation of mountain ranges. The concept of convection currents provides a tangible mechanism for understanding how the Earth's surface is dynamic and how the structure underneath influences global geological activity.