Final answer:
The lithosphere is divided into tectonic plates. The theory that describes their movement is plate tectonics. The movement of material due to density differences caused by temperature variations is called convection.
Step-by-step explanation:
1. The lithosphere is divided into pieces called tectonic plates. These plates are large areas of Earth's crust and upper mantle that fit together like puzzle pieces.
2. The theory that describes large-scale movements of Earth's lithosphere is called plate tectonics. This theory explains how the tectonic plates move and interact with each other, causing earthquakes, volcanic activity, and the formation of mountains and other geologic features.
3. The movement of material due to differences in density that are caused by differences in temperature is called convection. This process plays a key role in driving the movement of tectonic plates and the overall dynamics of Earth's geology.
Learn more about Tectonic plates and plate tectonics