Plate Tectonics - Understanding Global Change

Seashells in rocks on mountain tops, underwater mountain chains, and continents that look like giant pieces of a global puzzle provide evidence that Earth’s continents and seafloors move and change over time.

The theory of plate tectonics explains processes in the geosphere that are fueled by Earth’s internal heat that have operated over billions of years. These changes can be imperceptible over a human lifetime or violent and abrupt, and continue to shape Earth’s environments.

Global Change Infographic

The theory of plate tectonics explains process that shape the geosphere that are essential to How the Earth System Works. Click the image on the left to open the Understanding Global Change Infographic. Locate the plate tectonics icon and identify other Earth system processes and phenomena that cause changes to, or are affected by, plate tectonics.

What is plate tectonics?

As the young Earth cooled, layers formed and the most dense materials (primarily iron) sank to the middle (the core) of the Earth. Around the core formed the less dense layer called the mantle, topped by a thin layer called the crust. There are two kinds of crust: oceanic crust, which is found in ocean basins and the continental crust we live on that is made of lighter material than oceanic crust (to learn more about rock types, see the rock cycle page).

Cross section of Earth's outer layers. The lowest of these layers is shown in red and orange, and is labeled the asthenosphere. The next outermost layer is shown in khaki and is labeled the lithosphere. At the left side of the diagram, the lithosphere is covered by ocean and the thin layer between the khaki region and the ocean is labeled "oceanic crust." At right, is dry land, and the thicker, outermost layer of the Earth here is labeled "continental crust." Furthest left, there is a convergent plate boundary: one section of lithosphere is shown moving down beneath another, as the other pushes into it. Where the two plates meet beneath the ocean is a trench. Near this area, a stratovolcano extends up above the ocean's surface. This area is labeled "island arc." Moving right, there is a hotspot in the asthenosphere beneath a shield volcano midplate, with a red passageway connecting the asthenosphere to the tip of the volcano. Further right is a divergent plate boundary: two sections of lithosphere move away from each other and at this point, a red peak extends up from the asthenosphere to meet the ocean floor. This point is labeled "oceanic spread ridge." Further along this ridge is a transform plate boundary. Moving further right, one section of lithosphere (labeled "subducting plate") is shown moving down beneath another. At this point on the ocean floor is a trench, and this is labeled "convergent plate boundary." The contintental crust at right has a region of volcanoes and mountain ranges. Furthest right, two sections of lithosphere are shown moving away from each other with a red peak extending up from the asthenosphere between them. This is labeled "continental rift zone (young plate boundary)." At the top of the diagram, three types of plate boundaries are illustrated. A transform plate boundary is shown as two adjacent blocks moving past one another horizontally. Each block is made of a bottom portion that is red (the asthenosphere) and a top portion that is khaki (the plate). In a divergent plate boundary, two sections of khaki plate move away from one another atop a single wide brick of asthenosphere. In a convergent plate boundary, one section of khaki plate moves underneath another, protruding into the single wide brick of asthenosphere underneath it.

Modified from the USGS: Artist’s cross section illustrating the main types of plate boundaries (see text); East African Rift Zone is a good example of a continental rift zone. (Cross section by José F. Vigil from This Dynamic Planet — a wall map produced jointly by the U.S. Geological Survey, the Smithsonian Institution, and the U.S. Naval Research Laboratory.)

Although the crust and mantle are different in density and composition, the crust is attached to the uppermost part of the mantle, together forming the solid lithosphere. The lithosphere is broken up into huge sections, called plates that include both oceanic and continental crust. Below the lithosphere is a layer called the asthenosphere, which is a portion of the mantle that is weaker and less rigid due to pressure and temperature conditions. The rigid lithosphere moves on the asthenosphere both horizontally and vertically. Plates are constantly in motion, and move about 3 cm (a little over an inch) per year because of slow convection currents in the mantle due to Earth’s internal heat and pulling and pushing on the plates as they form, cool and sink back into the mantle. Through convection, hot regions of the asthenosphere heated from below rise closer to the surface, propelling the plates, and displace colder, denser material, which sinks back to lower parts of the mantle. Two additional processes, the sinking of old, cold and dense crust (slab pull), and the pushing of plates from ridges where plates form (ridge push), also contribute to plate movement.

World map showing that the Eurasian plate underlies western Eurasia (except India), Indonesia, and the northeastern Atlantic. The North American plate underlies the northwestern Atlantic, Greenland, North America, the northmost Pacific, and eastern Eurasia. The relatively small Filipino plate underlies the islands and ocean surrounding the Philippines. The Pacific plate underlies most of the central Pacific Ocean. The relatively small Juan de Fuca plate is sandwiched between the Pacific plate and the North American plate off the west coast of North America. The relatively small Cocos plate underlies the ocean off the west coast of Central America. The Nazca plate underlies the Pacific off the west coast of South America. The relatively small Caribbean plate underlies southern Central America and the Caribbean Sea. The South American plate underlies South America and the southwestern Atlantic Ocean. The relatively small Scotia plate underlies the southernmost part of the Atlantic Ocean. The African plate underlies Africa and surrounding portions of the Atlantic and Indian Oceans. The Arabia plate underlies the Middle East. The Indian plate underlies India and surrounding portions of the Indian Ocean. The Australian plate underlies Australia and surrounding portions of the Indian and Pacific Oceans. The Antractic plate underlies Antarctica and surrounding portions of the ocean.

Map of tectonic plate boundaries

Plates interact in three ways: 1) Plates move away from each other at what are called divergent boundaries (also known as spreading centers); 2) Plates move towards each other at convergent boundaries, where continents collide creating mountain ranges or one plate sinks beneath another plate at a subduction zones and can form volcanic arcs; 3) Plates slide past each other at transform boundaries creating strike-slip faults. The uplift and sinking of land, earthquakes (the sudden release of energy that causes shaking), and volcanic eruptions are all evidence of interactions and stress due to the movement of the plates. Plate motion may seem slow, but over millions of years plate tectonics shapes the distribution of continents and oceans and mountain ranges that shape diverse ecosystems and influence global climate.

Earth system models about plate tectonics

This Earth system model is one way to represent the essential processes that are related to plate tectonics, including Earth’s internal heat and the rock cycle. Hover over the icons for brief explanations; click on the icons to learn more about each topic. Download the Earth system models on this page.

Essential processes that are related to plate tectonics

Plate tectonics shapes global landforms and environments through the rock cycle, mountain building, volcanism, and the distribution of continents and oceans. These phenomena, ultimately driven by Earth’s internal heat, have far-reaching effects on other parts of the Earth system, including the sea level experienced along coastlines.

Some of the far-reaching effects of plate tectonics

How human activities are influenced by plate tectonics

Where and how humans live can be greatly affected by phenomena influenced by tectonic processes. Hover over or click on the icons to learn more about these Earth system connections.

Tectonic processes indirectly affect aspects of Earth systems that impact humans

Explore the Earth System

Click the icons and bolded terms (e.g. volcanism, rock cycle, etc.) on this page to learn more about these process and phenomena. Alternatively, explore the Understanding Global Change Infographic and find new topics that are of interest and/or locally relevant to you.

To learn more about teaching the plate tectonics, visit the Teaching Resources page.

Investigate

Learn more in these real-world examples, and challenge yourself to construct a model that explains the Earth system relationships.

Where did all of Madagascar’s species come from?

Understanding Global Change

On this page: