Science
What is plate tectonics?
Quick answer
Plate tectonics is the idea that Earth's outer shell is broken into huge slabs called plates that slowly move. Where they meet, mountains rise and earthquakes and volcanoes happen.
In one sentence
Plate tectonics explains that the ground beneath us is made of giant moving plates, and where they push, pull or slide, Earth's most dramatic events happen.
Explained
Earth's rocky outer layer, the crust together with the top of the mantle, is not one piece. It is cracked into about seven large plates and several smaller ones, like a broken eggshell. They carry the continents and the ocean floors. The plates rest on hotter rock beneath, called the mantle, which moves very slowly. Read about this in the layers of the Earth.
The plates creep along at a few centimetres a year, about as fast as your fingernails grow. You cannot feel it, but over millions of years it moves continents across the globe. About 250 million years ago, most land was joined in one supercontinent called Pangaea. It broke apart, and the pieces drifted to where they are now. The German scientist Alfred Wegener suggested in 1912 that the continents move. Evidence supports it: South America and Africa fit together like puzzle pieces, and the same fossils are found on both sides of the Atlantic.
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There are three kinds of boundary:
- Convergent: plates push together. Mountains rise, such as the Himalayas, where India meets Asia. One plate can also slide under another, creating deep ocean trenches and volcanoes.
- Divergent: plates move apart. New crust forms in the gap, like along the Mid-Atlantic Ridge, which is slowly widening the Atlantic Ocean.
- Transform: plates slide past each other. This can cause earthquakes, like along the San Andreas Fault in California.
Most earthquakes and volcanoes happen near the edges of plates. The Pacific "Ring of Fire" is a horseshoe of plate edges full of both. Plate tectonics is the reason the surface of our planet keeps changing.
Examples
| Boundary | What happens | Example |
|---|---|---|
| Convergent | collision or one plate sinking | Himalayas, Andes |
| Divergent | plates move apart | Mid-Atlantic Ridge, Iceland |
| Transform | plates slide sideways | San Andreas Fault |
Common mistakes
- "The plates are the continents." Plates include ocean floor, and a plate can carry both land and sea.
- "The ground floats on liquid lava." The mantle is solid rock that flows very slowly.
- "Continents moved fast." The speed is tiny, but the time is huge.
Quick quiz
Plate tectonics
Check what you know with 4 quick questions.
Question 1 of 4
About how fast do tectonic plates move?
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Related topics
Earthquakes
An earthquake is a sudden shaking of the ground. It happens when rocks along a crack in Earth's crust, called a fault, suddenly slip past each other.
Volcanoes
A volcano is an opening in Earth's crust where hot melted rock, gases and ash escape. Over time the cooled lava and ash can build a mountain.
Layers of the Earth
Earth has four main layers: a thin rocky crust, a thick mantle of hot rock, a liquid outer core and a solid inner core. Each layer is hotter than the one above it.
Tsunamis
A tsunami is a series of very long, fast ocean waves, usually caused by an underwater earthquake. They are small in deep water but can grow tall and powerful when they reach the coast.
Adaptation
An adaptation is a feature or behaviour that helps a living thing survive where it lives. A polar bear's thick fur and a cactus's spines are adaptations.
Amphibians
Amphibians are cold-blooded animals with thin, moist skin that live part of their lives in water and part on land. Frogs, toads, newts and salamanders are amphibians.