At a divergent boundary plates move apart; magma rises and new crust can form at mid-ocean ridges or continental rifts. At a convergent boundary plates move together; subduction can form trenches, deepening earthquake zones and volcanic arcs, while continent–continent collision can uplift fold mountains. At a transform boundary plates slide past, producing faults and frequent shallow earthquakes.
Plate motion is driven by interacting processes. Slab pull acts where cold dense oceanic lithosphere sinks; ridge push is gravity-assisted movement away from elevated ridges; mantle movement also interacts with plates. Avoid the oversimplification that plates float on a global ocean of liquid magma.
The theory is supported by converging evidence: Wegener’s continental-fit/fossil/rock/climate evidence, Marie Tharp’s seafloor maps, symmetric magnetic stripes and seafloor ages, earthquake/volcano belts, and modern GPS measurements.