Plate Tectonics

Plate tectonics is the scientific theory describing how Earth's outer shell (lithosphere) is divided into plates that move, collide, separate, and slide past each other over geological time. Alfred Wegener proposed continental drift in 1912 — noting how the continents fit together like puzzle pieces — but wasn't believed for 50 years. The theory was confirmed in the 1960s through seafloor spreading. Plate tectonics explains earthquakes, volcanic eruptions, mountain building, and ocean basins. The Himalayas formed where India collided with Asia; the Atlantic Ocean is widening by 2.5 cm per year; the Pacific Ring of Fire marks plate boundaries. Without plate tectonics, Earth would likely be geologically dead and uninhabitable.