Geographer — Lesson 3
Plate tectonics is the unifying theory of Earth science, explaining the distribution of earthquakes, volcanoes, mountain ranges, and ocean basins. Earth's lithosphere is divided into approximately 15 major tectonic plates and several smaller ones that move at rates of 1–10 centimeters per year. Key boundary forms include divergent boundaries (mid-ocean ridges) where plates move apart and new oceanic crust forms, convergent boundaries where oceanic crust subducts beneath continental crust forming deep ocean trenches, volcanic arcs, and mountain ranges, and transform boundaries where plates slide horizontally past each other.