Plate Tectonics

Plate tectonics is the unifying theory that Earth’s rigid lithosphere is broken into plates that move over the weaker asthenosphere, interacting at divergent (spreading ridge), convergent (subduction or collision), and transform boundaries. It explains seafloor spreading, the age-depth pattern of ocean crust, earthquake and volcano distributions, and the Wilson cycle of ocean-basin opening and closing. Magnetic-stripe symmetry across mid-ocean ridges was the decisive 1960s evidence.