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Earth's Tectonic Plates

heidi Kent, Rebecca Gillaspy
  • Author
    heidi Kent

    Heidi has taught middle school science, health, and English for more than 22 years. She has a Master's Degree in General Science from North Dakota State University. She is a member of the MSTA, has chaired Professional Development and Continuing Education at the Ashby Public School.

  • Instructor
    Rebecca Gillaspy

    Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

This lesson will cover what tectonic plates are, how many tectonic plates there are, where they are located, how they move, what their sizes are, and how they are named. Updated: 10/09/2021

Planet Earth and Plate Tectonics

Earth is a rocky, dense planet that formed about 4.6 billion years ago from molten material. This material has been cooling and settling ever since. At the center of the Earth lies the extremely hot and dense core. Surrounding the core lies the mantle, and above the mantle at the surface is the crust of the Earth. Their are two kinds of crust, denser, basaltic, oceanic crust which is found under oceans and continental crust which is less dense and mostly composed of granite. Another important layer identified by scientists is the lithosphere. This is the solid layer of Earth made of the rocky crust and the thin solid portion of the mantle just beneath it.

Scientists believe the solid lithosphere which covers the entire surface of Earth is actually broken into huge slabs called tectonic plates. 7 large major plates, 8 minor plates, and some very small micro plates make up the lithosphere of Earth.

Planet Earth

You are certainly familiar with the pictures of planet Earth showing its large land masses separated by brilliant blue oceans. In fact, if you were given a multiple-choice quiz right now, I bet you'd be able to identify the major land masses based on their shapes and locations. If you are from America, you might start by labeling North America and South America.

From there, you would probably be able to identify the big land mass to the east as Africa and the land mass that it wears as a hat as Europe. From Europe, it's a short trip east to Asia, which snuggles up to India at its base. The big continent at the bottom of the globe is easily recognized as Antarctica, and by process of elimination, you would label the remaining area as Australia.

But is this always the way planet Earth has looked? According to geologists, at one time, these major land masses were all bunched together as one big supercontinent. This supercontinent then broke apart, and over time, the continents drifted into their current locations.

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  • 1:12 Plate Tectonics
  • 2:24 North American and…
  • 3:14 Pacific Plate
  • 3:47 African and Eurasian Plates
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This is a simple representation showing layers within the earth. Heat moves from the center outward and creates movement of the outer layer.

Earth:  Simple Cross Section

Movement of Tectonic Plates

The solid tectonic plates of the lithosphere float on top of a softer layer of the mantle that can flow or move. It is the heat from the core transferring through the mantle that causes this soft layer to flow. These convection currents in the mantle in turn move the tectonic plates lying on top.

Scientists use data showing the locations of earthquakes and volcanoes, the ages of rock and fossils on different continents, and more to explain the existence of tectonic plates and how they change in position and size. This is the basic principle of the Theory of Plate Tectonics.

How Many Tectonic Plates are there?

Scientists identify 7 major tectonic plates. In order from largest to smallest they are: the Pacific Plate, the North American Plate, the Eurasian Plate, the Antarctic Plate, the Indo-Australian Plate, and the South American Plate. Each plate is named based on what lies above it. For example, North America lies on top of the North American Plate, Europe and Asia are located above the Eurasian Plate, and so on.

In addition to the 7 major plates, there are also 8 minor plates which are much smaller in size. The map below shows all the major plates and some of the minor ones as well. The map also shows the Indian Plate and Australian Plate as separate, however they are usually considered to be one plate called the Indo-Australian Plate. The arrows on the map indicate the directions the plates are moving. At some boundaries crust is created, at others it is destroyed.

Boundaries of major plates and some minor plates are shown as dark lines extending beyond the actual countinents. Note that the Indian and Australian plate on the map are often considered to be one plate called the Indo-Australian Plate.

Tectonic Plates

Major Tectonic Plates

Of the 7 major tectonic plates, the largest is the Pacific Plate which is more than twice the size of the smallest major plate, the South American. Listed below are the sizes according to the World Atlas.

List of Major Tectonic Plates and Size in Millions of Kilometers

  • Pacific Plate: 103.3
  • North American Plate: 75.9
  • Eurasian Plate: 67.8
  • African Plate: 61.3
  • Antarctic Plate: 60.9
  • Indo-Australian Plate: 58.9
  • South American Plate: 43.6

The thickness of tectonic plates ranges from 15 km to 200 km. The thinnest being new oceanic crust and the thickest being mountainous regions of older continental crust.

There are also minor plates that range in size from 1.1-16.7 million kilometers. One of the smallest plates, called a micro-plate, is the geologically active Juan de Fuca Plate located in the Pacific Northwest. It is just 250,000 square km.

Pacific Plate

The Pacific Ocean lies above the Pacific Plate. It is the largest tectonic plate and the only one covered almost entirely by water. This large, dense plate collides with surrounding plates and has created 'The Ring of Fire,' a zone of active volcanoes located around much of the Pacific Plate. This is shown marked in red on the map below.

Another notable feature created by collisions with the Pacific Plate is the Mariana Trench. It is the deepest known spot in the ocean. This spot is also labeled on the map below.

Around the convergent boundary of the Pacific Plate lies a band of active volcanoes known as the Ring of Fire. Also labeled is the Mariana Trench, the deepest spot in the ocean.

Pacific Plate:  Ring of Fire and Mariana Trench

North American and South American Plates

The North American Plate lies beneath North America, Greenland, and part of Iceland. It extends from the western edge of the continent out into the middle of the Atlantic Ocean at its eastern boundary. This boundary is formed by the Mid-Atlantic Ridge, a large underwater chain of mountains created by magma and lava moving up through the crack between between plates. This is how Iceland, which is actually an underwater mountain, formed. Iceland lies on both the North American Plate and the Eurasian Plate.

The western side of the North American Plate is geologically active, as plate boundaries often are. Shown in the map of the North and South American plates are the surrounding plates with the red arrows indicating the direction of their movement. Plate interaction can create seismic and volcanic activity. At the San Andreas fault in California, many earthquakes occur as the Pacific Plate grinds past the North American Plate. The Appalachian and Rocky Mountains were also built by the pressure of tectonic activity.

Plate Tectonics

How this drifting apart of major land masses occurred was a mystery for many years and highly debated among scientists. But when the theory of plate tectonics was introduced, much of the debating quieted down. Plate tectonics is the theory that Earth's crust is broken up into plates.

It is as if the planet's surface is cracked, much like the cracks that would form on the outside of a hardboiled egg if you were to drop it. These large cracks in the earth's surface form plate-like sections of Earth's crust referred to as tectonic plates.

These plates are actually pieces of the planet's lithosphere, which is the outermost shell of the earth made up of the earth's crust and upper part of the mantle, and for this reason, tectonic plates are sometimes called 'lithospheric plates.' These plates float on top of the hotter and more fluid asthenosphere, which is the layer below the lithosphere. There are seven major tectonic plates that very slowly move around on the surface of our planet along with a number of minor plates. Let's take a look at the seven major plates of the lithosphere.

North American and South American Plates

At the start of this lesson, we identified some major land masses found on Earth. This gets us closer to understanding the location of the major tectonic plates, but it doesn't share the whole story. This is because tectonic plates can contain both continental crust and oceanic crust. Therefore, some of the plates may contain land, but others may be located underwater or be a mix of both.

Take the North American plate for example. It is one of the major plates of the lithosphere and extends from the middle of the Atlantic Ocean to the West Coast of North America. The same can be said for the South American plate, which is another of the seven major plates and extends from the middle of the Atlantic Ocean to the west coast of South America.

Pacific Plate

So, you can see below that the North and South American plates contain oceanic crust, even though they are named for the main continent they encompass. In fact, six of the seven major tectonic plates are named after the continents they contain. The one exception is the Pacific plate, which lies beneath the Pacific Ocean. Not only is this the only major tectonic plate that is mainly underwater, it is also the largest, spanning over 100 million square kilometers.

The majority of plates are named after the continents they contain.
pacific plate diagram

African Plate and Eurasian Plate

Tectonic plates border each other.
tectonic plate borders

Now, you might be noticing above that these major tectonic plates bump up against each other. When tectonic plates meet, they become a site for tectonic activity. Depending on whether the plates are moving toward each other, sliding past each other or pulling apart, tectonic activity might include mountain building, earthquakes, tremors or volcanoes.

In the southern Atlantic Ocean, we see below that the South American plate meets the African plate, which is the major plate that includes Africa and surrounding oceanic crust. They meet at the Mid-Atlantic Ridge, which is a large underwater mountain range on the floor of the Atlantic Ocean caused by diverging tectonic plates.

The African plate is the major plate that includes Africa.
african plate

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Video Transcript

Planet Earth

You are certainly familiar with the pictures of planet Earth showing its large land masses separated by brilliant blue oceans. In fact, if you were given a multiple-choice quiz right now, I bet you'd be able to identify the major land masses based on their shapes and locations. If you are from America, you might start by labeling North America and South America.

From there, you would probably be able to identify the big land mass to the east as Africa and the land mass that it wears as a hat as Europe. From Europe, it's a short trip east to Asia, which snuggles up to India at its base. The big continent at the bottom of the globe is easily recognized as Antarctica, and by process of elimination, you would label the remaining area as Australia.

But is this always the way planet Earth has looked? According to geologists, at one time, these major land masses were all bunched together as one big supercontinent. This supercontinent then broke apart, and over time, the continents drifted into their current locations.

Plate Tectonics

How this drifting apart of major land masses occurred was a mystery for many years and highly debated among scientists. But when the theory of plate tectonics was introduced, much of the debating quieted down. Plate tectonics is the theory that Earth's crust is broken up into plates.

It is as if the planet's surface is cracked, much like the cracks that would form on the outside of a hardboiled egg if you were to drop it. These large cracks in the earth's surface form plate-like sections of Earth's crust referred to as tectonic plates.

These plates are actually pieces of the planet's lithosphere, which is the outermost shell of the earth made up of the earth's crust and upper part of the mantle, and for this reason, tectonic plates are sometimes called 'lithospheric plates.' These plates float on top of the hotter and more fluid asthenosphere, which is the layer below the lithosphere. There are seven major tectonic plates that very slowly move around on the surface of our planet along with a number of minor plates. Let's take a look at the seven major plates of the lithosphere.

North American and South American Plates

At the start of this lesson, we identified some major land masses found on Earth. This gets us closer to understanding the location of the major tectonic plates, but it doesn't share the whole story. This is because tectonic plates can contain both continental crust and oceanic crust. Therefore, some of the plates may contain land, but others may be located underwater or be a mix of both.

Take the North American plate for example. It is one of the major plates of the lithosphere and extends from the middle of the Atlantic Ocean to the West Coast of North America. The same can be said for the South American plate, which is another of the seven major plates and extends from the middle of the Atlantic Ocean to the west coast of South America.

Pacific Plate

So, you can see below that the North and South American plates contain oceanic crust, even though they are named for the main continent they encompass. In fact, six of the seven major tectonic plates are named after the continents they contain. The one exception is the Pacific plate, which lies beneath the Pacific Ocean. Not only is this the only major tectonic plate that is mainly underwater, it is also the largest, spanning over 100 million square kilometers.

The majority of plates are named after the continents they contain.
pacific plate diagram

African Plate and Eurasian Plate

Tectonic plates border each other.
tectonic plate borders

Now, you might be noticing above that these major tectonic plates bump up against each other. When tectonic plates meet, they become a site for tectonic activity. Depending on whether the plates are moving toward each other, sliding past each other or pulling apart, tectonic activity might include mountain building, earthquakes, tremors or volcanoes.

In the southern Atlantic Ocean, we see below that the South American plate meets the African plate, which is the major plate that includes Africa and surrounding oceanic crust. They meet at the Mid-Atlantic Ridge, which is a large underwater mountain range on the floor of the Atlantic Ocean caused by diverging tectonic plates.

The African plate is the major plate that includes Africa.
african plate

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