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Earth’s lithosphere is fractured into tectonic plates that move slowly over the asthenosphere, with motion typically ranging from ~0 to 10 cm per year.
Plate tectonics is the scientific theory that Earth’s rigid outer shell (the lithosphere) is broken into large tectonic plates that move slowly over geologic time. The model developed from continental drift and was widely accepted after mid- to late-1960s validation of seafloor spreading. The lithosphere—cooler and more rigid than the underlying asthenosphere—rides on a weaker, viscoelastic layer, and plate motion is typically on the order of centimeters per year. Where plates meet, their relative motion creates three main boundary types: divergent (plates move apart, forming new crust at spreading centers), convergent (plates move together, often producing subduction zones and trenches or continental collisions that build mountains), and transform (plates slide past each other along transform faults). These boundaries are associated with major geologic activity such as earthquakes, volcanism, mountain building, and trench formation. Plate motion is driven largely by density contrasts and mantle dynamics—especially the sinking of older, denser oceanic lithosphere at subduction zones (slab pull) and the cooling/thickening of oceanic lithosphere that contributes to ridge push/gravitational sliding—while other mechanisms (e.g., mantle convection patterns, upwelling, and debated contributions like tidal drag) are discussed in ongoing research.
Earth’s lithosphere is fractured into tectonic plates that move slowly over the asthenosphere, with motion typically ranging from ~0 to 10 cm per year.
Plate boundaries are classified as divergent, convergent (subduction or collision), and transform, and each type produces characteristic landforms and hazards (e.g., ridges, trenches, earthquakes, volcanism).
Oceanic and continental lithosphere differ in composition and density; oceanic crust forms at spreading ridges, cools and thickens with age, and is largely recycled through subduction to help keep Earth’s surface area roughly constant.
Earth’s rigid outer shell, including the crust and upper mantle, that is broken into tectonic plates.
A hotter, weaker, ductile layer beneath the lithosphere that allows plate motion.
A large, relatively rigid slab of lithosphere that moves over the asthenosphere.
A plate boundary where plates move apart, commonly forming seafloor spreading centers and new oceanic crust.
A plate boundary where plates move toward each other, producing subduction zones or continental collisions.
A plate boundary where plates slide past each other along transform faults without creating or destroying lithosphere.
A convergent boundary where a denser plate (often oceanic lithosphere) sinks into the mantle beneath another plate.
The process by which new oceanic crust forms at mid-ocean ridges and spreads outward as older crust is carried away.
A major driving force in plate tectonics where the weight of cold, dense subducting oceanic lithosphere pulls plates toward subduction zones.
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