Layers of the Earth

As we all know, the Earth is round.  One thing we may not all know though is that the Earth is not just one giant rock like it looks.  The truth is, the Earth is made up of many different layers and parts.  Some parts of the Earth never stop moving.


When some people describe the Earth, they sometimes describe it like an onion.  If you have ever peeled an onion and really looked at it, you would see that an onion has many different layers.  The top layer is usually a dark yellow and this normally the first or outer layer of the onion.  The more you peel it, the more layers that you will see until you get into the center of the onion which is oftentimes a solid, white, small ball.

Structure of the Earth

The Earth is a lot like an onion because if you were to peel apart the Earth, you would see that it was in different layers.

Layers of the Earth

There are four layers of the Earth that are the main layers, and these include:

  • Crust
  • Mantle
  • Outer Core
  • Inner Core

How Were the Layers of the Earth Formed?

Billions and billions of years ago, the Earth was made, and it was very hot.  As the layers began to cool, the outside layer would become hard and then the inside of the Earth stayed hot.

Mapping the interior of Earth with earthquake waves.

The Earth’s Crust

The crust is the outer most layer of the Earth.  This layer is thinner than the other layers and it is about 5 kilometers to 70 kilometers thick.

We live on what is called the continental crust which is part of the layer of the Earth.  The continental crust is made up of different rocks but mostly of silica and alumina.  The silica and alumina of the Earth’s Crust is called “sial.”

Schematic view of the interior of Earth

The crust is the layer of the Earth that people live on.  The crust also has the sea, soil, mountains, oceans and more.  The crust is around 305 miles thick in the ocean.

Oceanic Crust

The part of the Earth where the ocean sits is called the oceanic crust.

Continental Crust

The part of the Earth that we walk on and grow plants and trees is called the continental crust.

What is the Crust Made Of?

The crust is made up of different kinds of rocks, some even being igneous rocks.  Some of the rocks that are included in the make up of the crust include:

  • Basalt Rock
  • Granite

How Big is the Crust?

The Earth’s crust is around 25 miles thick.

What is Interesting About the Earth’s Crust?

One thing that is very interesting about the crust of the Earth is that it is the only layer of the Earth that people can drill and look at.

The Mantle

The mantle is the part of the Earth’s that is between the crust and the outer core.  The mantle is thicker than the crust and can be over 3000 kilometers thick.  This part of the Earth is made up of silicate rocks that have a lot of magnesium and iron in them.

Even though the mantle is solid, it is not completely solid.  Since there is so much heat and pressure, it keeps the layer from getting completely hard.  If you were able to feel the mantle, some believe that it would feel like clay.

Many scientists put the mantle into two different categories; the upper mantle and the lower mantle.  There are only tiny differences between the two mantles.

The main difference between the upper and lower mantle is that the upper mantle has a special rock called olivine.  Olivine is made up of silicon dioxide and peridotite.  Peridotite is a very heavy rock.

The lower mantle is stronger and is solid.  It is made up of:

  • Ovalene
  • Iron
  • Magnesium
  • Silicate

The mantle has semi-solid rocks that can turn into liquid if there is enough pressure.  When the rocks get very hot and then get very cool, it causes them to sink back into the core and this is what causes the crust to break into different plates and sections.  When these plates and sections move, it is what causes there to be different things that happen on the Earth such as earthquakes and volcanic activity.

Sometimes, the magma that is found in the mantle can get so hot and full of pressure that it travels up and out of the crust of the Earth.  This is why volcanoes erupt.

The Outer Core

The outer core is located between the mantle and the inner core of the Earth.  The outer core is mostly made up of nickel and iron and is more than 4000 degrees Celsius, so it is extremely hot.  The nickel and the iron are in liquid form because of it being so hot in the outer core.

The outer core creates a magnetic field, must like the North and South Pole do.  The magnetic field helps to protect the Earth from so much sun radiation and from solar winds that could damage the Earth.  The magnetic field of the outer core goes all the way into space, so the Earth is very protected.

Shape of the Outer Core

The outer core is outside of the inner core and it is shaped like a sphere.  In the outer core, there is a lot of pressure, not as much as the inner core but still a lot of pressure.

What is the Outer Core Made Of?

The outer core is made up of molten iron which is also written in the formula of Fe.  Since it is made up of molten iron, the outer core is very magnetic.  The reason that the outer core is magnetic is because of all of the magnetic liquid that is constantly flowing in the outer core.

How Big and How Hot is the Outer Core?

The outer core is 3,200 miles thick and is between 7,200 degrees Fahrenheit to 9,000 degrees Fahrenheit.

The Inner Core

The Inner Core is located inside the outer core.  Like the outer core, the inner core is also made up of nickel and iron but instead of it being a liquid, it is a solid.  Even though the inner core is very hot just like the outer core, there is a lot of pressure that is applied from all of the other Earth’s layers.  Because of the pressure, it causes the nickel and the iron to be solid.

The inner core, even though the nickel and iron are solid, it is the hottest part of the Earth and it is over 5000 degrees Celsius.

Some interesting things about the inner core of the Earth is that the inner core has more pressure than all of the other layers.  Since the inner core is so small compared to the other layers, it is more compacted by the weight of the other layers.


The core is very dense which means that it is close together or compacted and this is because it is mostly made up of iron, but it is not made up of pure iron.

How Big and How Hot is the Inner Core?

The inner core is around 1,500 miles thick and is between 9,000 degrees Fahrenheit and 13,000 degrees Fahrenheit.

What Makes the Inner Core Different?

The inner core is different because it always spins at a speed that is different than what the rest of the Earth is spinning at.

Another thing that makes it different is that even though it is really hot in the center of the Earth, it will never melt because there is so much pressure on it that it stays solid.

How Do Scientists Know There are Different Layers?

Scientists know that there are different layers because they study waves.  These waves are called seismic waves.  Waves like these happen when there is an earthquake or a volcanic eruption or when the ocean moves in a certain way.

Seismic Waves

There are two different kinds of seismic waves:  shear waves and pressure waves.

  • Shear waves-A shear wave will not travel through liquid
  • Pressure waves-A pressure wave travels through both liquid and solids.

More Facts About Layers of the Earth:

  • Sea floors are made when the basalt rock presses into the mantle and the mantle fills with water.
  • Some continents are lighter and float on the mantle like ice in a cup float.
  • Machines that measure seismic waves are called seismographs.
  • Some scientists believe that meteorites are pieces of planets that have blown up.
  • The inner and outer core of Earth are as big as the planet Mars.

What Did You Learn?

  • What are layers of the Earth?
    The layers of the Earth are the different layers that make up the Earth that we live in.  These layers include the core, mantle, outer core and the inner core.
  • What layer of the Earth is solid even though it is hot enough to melt?
    The layer of the Earth that is hot enough to melt but is solid is the inner core.
  • What layer of the Earth is moldable like clay?
    The mantle, even though it is hard, it is not solid.
  • What is the layer of the Earth that we walk on?
    The layer of the Earth that we walk on is the crust, also called the continental crust.
  • How do scientists know that the Earth has different layers?
    Scientists know that the Earth has layers because of seismic waves.