Plate Tectonics Science

Plate tectonics — the theory that Earth's lithosphere is divided into large plates that move relative to each other at 2–10 cm per year — is the unifying theory of geology. Proposed by Alfred Wegener in 1912 as 'continental drift' (based on the jigsaw puzzle fit of continents), it was ridiculed for 50 years until seafloor spreading was discovered in the 1960s. Plate tectonics explains the distribution of earthquakes and volcanoes (along plate boundaries), mountain formation (collision of plates produces Himalayas, Alps, Rockies), island arcs (Japan, Philippines, Aleutians), and ocean formation. The Pacific 'Ring of Fire' — 90% of the world's earthquakes — marks the edges of the Pacific Plate. All continents once formed a single supercontinent, Pangaea, that broke apart 175 million years ago.