The Online Library of Knowledge

Planet Earth

Plate tectonics

A cross-section through the Earth's crustA cross-section through the Earth's crust The Atlantic Ocean gets wider by about the width of your thumb every year, pushing North and South America away from Europe and Africa. The Himalayan mountains, already the highest in the world, grow taller by about the length of your thumb every year. Many other parts of the Earth are moving and changing shape, too. This is because the Earth’s outer layer is divided into enormous curved pieces called tectonic plates, which fit together like a ball-shaped jigsaw. There are six large plates and about 12–15 smaller ones, and they are continually on the move, pulling apart, bumping together or sliding past each other. The movements and collisions along the edges of the plates cause volcanoes and earthquakes. They also build mountains. Scientists call these movements plate tectonics.



The Earth's tectonic platesThe Earth's tectonic plates

Continental drift

Each plate consists of a piece of the Earth’s outer layer, the crust, plus a thin layer of outer mantle that lies beneath it. Together they make up the layer known as the lithosphere. Its depth varies from 70–80 kilometres (40–50 miles) below the oceans to 100–150 kilometres (60–90 miles) below the continents.

Under the lithosphere is a slightly deeper part of the mantle about 100 kilometres (60 miles) thick, called the asthenosphere. This is partly molten and allows the plates to slide about over it. In fact, the flowing motion of the mantle, due to the enormous heat and pressure within that layer, pushes the plates and makes them slide around the globe. As they do so, they carry the continental land masses like giant rafts. This is called continental drift. A map of tectonic platesA map of tectonic plates

The Himalayan mountains grow taller by about the length of your thumb every year.

© 2019 Q-files Ltd. All rights reserved. Switch to Mobile