Set 2: Central Ideas (Intermediate)

PASSAGE

The following text discusses plate tectonics. Plate tectonics is a scientific theory describing the large-scale motion of seven large plates and the movements of a larger number of smaller plates of Earth's lithosphere. The theory builds on the concept of continental drift, an idea developed during the first decades of the 20th century. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries.