How plate tectonics works — Earth science, 14–17 years
Earth’s outer shell is broken into moving plates. Their slow movement builds mountains, opens oceans and causes many earthquakes and volcanoes.
The moving skin of Earth
Earth’s rigid outer layer is cracked into huge pieces called tectonic plates. They float on hotter, softer rock below and move only a few centimetres each year. Where plates meet, they can pull apart, collide or slide past one another.
Why this idea was needed
Continents seemed to fit together, and matching fossils and rocks appeared on shores now far apart. Earlier explanations could not show how continents moved. Plate tectonics solved that problem by treating continents as parts of moving plates, powered mainly by heat escaping from Earth.
Reading a plate boundary
Imagine an oceanic plate moving towards a continental plate. The denser oceanic plate bends and sinks beneath the continent: this is subduction. Water and heat help melt rock, so magma rises to form volcanoes, while the locked boundary can produce strong earthquakes.
The map is not the motion
A common mistake is to think continents move across fixed ocean floors, like boats on water. That seems reasonable because maps show continents as separate shapes. In reality, oceanic crust is part of the moving plate too, and new crust forms at some boundaries while old crust sinks at others.
Why it matters
Scientists use plate maps to estimate where earthquakes, volcanoes and tsunamis are more likely, though they cannot predict the exact day of an event. Engineers use this knowledge when designing buildings and roads. It also explains why mountain ranges and ocean trenches occur in particular places.
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