Plate Tectonics

Plate Tectonics is the theory that the outer area of the Earth is made of different plates that are always moving.  The land and the water sit on these plates.  Under the plates is lava and melted rock.  Even though the plates are made of solid rock, they move on the liquid underneath.  The plates are always moving.

The tectonic plates of the world were mapped in the second half of the 20th century.

Different Plates

Some scientists believe that there are seven or eight major plates that make up the plate tectonics of the Earth.  There are also other plates that are minor plates that are hooked on to the major plates.

Convergent boundary

Each year, these plates move about one centimeter so even if you watched it for the whole year, you would not even know that it moved.

Major Plates

The seven different major plates include:

  • Eurasian
  • North America
  • South America
  • Africa
  • Antarctic
  • India-Australian
  • Pacific Plates

Transform boundary

Minor Plates

Some of the minor plates include:

  • Scotia
  • Arabia
  • Caribbean
  • Nazca
  • Scotia

Types of Plates

There are two different types of tectonic plates including oceanic and continental plates.  The plates are more than 60 miles thick.

  • Oceanic plates-The oceanic plates are made up of magnesium and silicon.  The crust of these plates is called “sima” after the silicon it is made up of.
  • Continental plates-The continental plates are made up of silicon and aluminum.  The crust of these plates is called “sial” which is named after the elements it is made of.

Plate Boundaries

There are three different types of boundaries in which the plates move, and these include convergent boundaries, divergent boundaries and transform boundaries.

Convergent Boundaries

Convergent boundaries are the places where the two plates will push together or move under each other.  When the plates move under each other it is called subduction.  The movement can be slow and can be where volcanoes and mountains are formed.

Divergent Boundaries

Divergent boundaries happen hen the two plates are pushed apart.  When there is land and this happens, it is called a rift.  New land can be made when magma goes from the mantle and reaches the surface and cools down.

Transform Boundaries

When the plates slide past each other, this is called a transform boundary.  These are also called faults and happen usually after an earthquake has happened.


The only way that you could really see the plate tectonics move would be if there was an earthquake.  When an earthquake happens, it causes the plates to move and to even stack on top of each other.

Fault lines are where earthquakes and volcanoes are.  This is where much of the activity happens.

The “Ring of Fire” is an area of all kinds of volcanic activity and earthquakes that is caused by a lot of tectonic plate movement.

The Hawaiian Islands are not part of the “Ring of Fire,” but are called hot spots because this is where magma rises up from the crust of the Earth through volcanoes.

Layers of the Earth

The plates are what make up the lithosphere or the top layer of the Earth.  The layer under the lithosphere is called the asthenosphere.


The asthenosphere is a layer of the Earth that is covered in molten rock.  This rock is liquid and the rocks on these.  This layer of the earth has constant radiation and heat that is hitting it from the center of the Earth.  As this heat and radiation hits the rocks, the rocks become melted and turn to liquid.

The tectonic plates are floating on these rocks and are always moving around the Earth.  This is like ice that floats on top of water.

Continental Drift

When the tectonic plates are always moving, this is called the continental drift.

Spreading Center

Since the rocks are constantly floating on liquid, sometimes they spread apart.  When the plates spread apart from each other, this is called the spreading zone.

Subduction Zone

When the plates are not spreading apart, they are moving closer together.  When the plates are moving together, this is the subduction zone.

Zone of Convergence

When the plates are forced together, they are in the zone of convergence.  When this happens, usually one plate will move under the other plate.  When the plates get pushed down on one side, that side will go into the asthenosphere where it is hot, and that part of the plate will melt.

When the plate melts, this causes there to be a crack or a trench in the plate.  These trenches or cracks are found in the deepest parts of the ocean.  The trenches can be so deep that it causes the ocean to flow into them and that is where the ocean is the deepest.

The Science Behind Plate Tectonics

Scientists have been able to look at the Earth for millions of years back because of scientific things such as maps, fossils and other evidence.

Because of this scientific evidence, scientists have been able to prove that the theory of tectonic plates is real.

Scientists were able to look at the map of the continents and see how the tectonic plates have caused the continents to form together almost like a puzzle.


Some scientists believe that the Earth used to be just one giant land mass.  This was called Pangaea.  Pangaea is a super-continent where there were no lines but just one complete land mass.  Some scientists believe this happened over 500 million years ago.


Different fossils have been found on different continents.  For example, one fossil was found on Australia that was the same as some of the fossils in Asia.  This proved that the planets were once all together and were one piece.

Some scientists believe that the continents used to all share the same area and that there were plats that were on the super-continent and when the continents split apart, new plants were formed.


Some believe that mountains are formed by plates that move and crash into each other.  When this happens, the edges of the plate will sometimes rise up and this is where mountains are formed.

More Facts About Tectonic Plates:

  • San Andreas Fault that is located in California is a transform boundary.
  • The San Andreas Fault causes many of the earthquakes that California has.
  • The deepest part of the ocean or the ocean trench is called the Mariana Trench.  This happened because of a convergent boundary that happened in the Pacific Ocean.  The Pacific Plate is being subducted or pushed together with the Mariana Plate to form this trench.
  • When the Indian Plate and the Eurasian Plate pushed together, it caused Mount Everest and the Himalayan Mountains to be formed.
  • Plate tectonics are sometimes called crustal plates.
  • The first person to talk about tectonic plates was Alfred Wegener, a German geophysicist.
  • Alfred Wegener called the super continent Pangaea.
  • Some of the fossils found on different planets included the Cynognathus which was a reptile, and the glossopteris which was a plant.
  • Sea floor spreading is when the ocean floor spreads out form the center and the land around it sinks.
  • The continental crust is not as dense as the oceanic crust.
  • Convection heat happens from radioactive elements such as uranium and potassium in the asthenosphere.
  • Plate boundaries are the areas where the tectonic plates are split.
  • Some scientists believe that tectonic plates move because of the magnetic field.

What Did You Learn?

  • What are tectonic plates?
    Tectonic plates are plates that move around on the liquid that is under the crust of the Earth.
  • Why are the tectonic plates important to understand?
    It is important to understand tectonic plates because that is how some mountains and some deep parts of the ocean are formed.
  • What are the two types of plates?
    The two types of plates are major and minor plates.  There are around 7 or 8 major plates and many minor plates.
  • What is it called when two plates move closer to each other?
    When two plates move closer to each other this is called subduction.
  • What is it called when the plates overlap and one part of the plate melts in the hot liquid under the crust?
    This is called the zone of convergence.