Tectonic activity refers to the movement and interaction of the Earth's tectonic plates, which comprise the Earth's lithosphere. This activity results in various geological phenomena such as earthquakes, volcanoes, and the formation of mountain ranges. Tectonic processes are driven by forces within the Earth, including mantle convection and the heat generated by radioactive decay. The theory of plate tectonics explains how these plates drift, collide, and separate over time, significantly shaping the planet's landscape and affecting geological and biological evolution.