Plate Tectonics – Earth Science

How did Earth get to look the way it does today? What made the mountains and what causes earthquakes? The answer is the theory of plate tectonics.

The Earth’s crust and the uppermost part of the mantle make up the lithosphere. The theory of plate tectonics states that the lithosphere is made up of different plates that push and rub up against each other.

The area beneath the lithosphere is called the asthenosphere. It moves around and causes the plates of the lithosphere to collide.

Plate Tectonics


People have always wondered how the Earth got its shape and features. There were many different ideas. In 1912 German scientist Alfred Wegener came up with a theory that the continents slowly moved.

Other scientists built on this theory of continental drift, eventually coming up with the theory of plate tectonics. Scientists still debate today about the specifics of plate tectonics. 

Plate Boundaries

The lithosphere is made up of major and minor plates that are always moving. The fastest moves at about 6 inches a year, while the slowest moves at about 1 inch a year.

Convergent Boundary

The boundaries between plates can be broken down into three groups: convergent, divergent, and transform plate boundaries.

Convergent boundaries are where two plates push into each other. One plate is pushed underneath the other plate and a section of the Earth’s crust is returned to the mantle. Convergent boundaries are where you find mountains and volcanoes.

Divergent boundaries are where two plates are pushing away from each other. This creates new sections of the Earth’s crust.

Transform plate boundaries are where two plates slide alongside each other. This move causes earthquakes and tsunamis.

Divergent Boundary

Tectonic Features

Tectonic plates are pushing new crust at areas called rift zones, or mid-ocean ridges. These are found at divergent boundaries. The hot mantle pushes lava to the surface, where it cools and creates new ocean floor. As new crust is formed plates are forced to move to make space.

The Earth’s crust is returned to the mantle at subduction zones. The plates collide and push the cooler, thinner crust beneath the thicker plate.

When two thicker continental plates meet, large mountain ranges are formed. The continents crust of India and Asia collided 55 million years ago creating the Himalayan mountain range.

Convergent boundaries can also be found in the ocean. When they meet they can create volcanoes that eventually turn into islands. Japan is an example of such a meeting.

The San Andreas Fault is one of the most famous examples of a transform plate boundary. The San Andreas Fault is a strike-slip fault that doesn’t create mountains or volcanoes, but instead creates massive earthquakes.

Interesting Facts

  • The Pacific Plate is the largest plate, measuring at about 40,000,000 square miles
  • The deepest point on Earth, the Mariana Trench, is created by an ocean-ocean convergence
  • The Ring of Fire is a network of subduction zones with incredible volcanic activity around the Pacific Ocean
  • You can walk on newly created crust in Iceland, where the North American Plate and the Eurasian Plate are growing apart from each other

Earth Science