The Interior of the Earth

By Moira Whitehouse PhD

The surface of the Earth is constantly changing as new landforms are built and older ones are destroyed by the forces of the Earth.

On the other hand, volcanic eruptions and earthquakes can change the surface of the Earth very quickly.

Some changes happen so slowly that you do not see the differences for a long time—for example the Colorado river carving the Grand Canyon has been happening for millions of years.

How are Landforms Made?• Now let’s examine the forces that create the different landforms. Broadly speaking, there are two kinds:

•Constructive forces—those that build up theland.

• Destructive forces—those that wear down the land.

To understand the constructive forces of the Earth—the ones that build up landforms, we need to understand what the interior (the inside) of the Earth is like.

What’s inside the Earth?

If you were able to cut the Earth in half, you would find it is made up of different layers.

Let us look at the inside of the Earth.

NASA image

Crust

The thin, outermost layer of the earth is made of solid rock and is called the crust.

All of the landforms on Earth are located on the crust and all life on Earth exists on this top layer.

The Earth’s crust consists of the oceanic and the continental crusts, both of which float on the magma (melted rock).

• The continental crust is the layer of rock which forms the continents and those areas of shallow seabed close to the shore. The continental crust is much thicker than the oceanic crust--about 19 miles thick.

• The oceanic crust is the layer of rock which forms the floor of an ocean. It is about 4-7 miles thick.

magma

The oceanic crust is made of mostly basalt, a very dense rock that is much heavier than the granite of the continental crust.

As a result, the oceanic crust sinks deeper into the magma (the molten rock) when the continental and oceanic crust meet.

The continental crust is mainly made of a rock called granite.

magma

This rock is mainly granite.

This rock is mainly basalt.

The mantle is the layer directly below the crust.

• It is about 1800 miles thick and made of melted rock.

NASA image

As you get closer to the center of the Earth the hotter it is. This explains why the rock in the mantle is molten (melted).

The cooler (heavier) melted rock in the mantle sinks as the hotter (lighter) melted rock rises, creating convection currents.

http://www.freedigitalphotos.net

Below the mantle is the core, the center of the earth.

The core is also divided into two regions, the inner core and the outer core. Scientists believe the outer core is a liquid and the inner core is a solid.

Outer core, liquid iron

Inner core, solid iron and nickel

http://scign.jpl.nasa.gov/

Remember that landforms are found on a very thin crust floating on top of a thick layer ofmolten (melted) rock called magma.

Let’s see how the make-up of this planetary ball affects how some landsforms are created.

Plates Make up the Crust of the Earth

Next, the crust of the Earth is broken into huge pieces of rock called plates. These plates fit together around the globe like a giant jigsaw puzzle.

The plates float on the hot, melted rock found in the mantle.

Creative CommonsWikipedia Commons

• We learned that because of convection the magma below the magma flows, very slowly, in large patterns.

Creative CommonsWikipedia Commons

Because of convection, the cooler (heavier) melted rock in the mantle sinks as the hotter (lighter) melted rock rises creating convection currents. These currents rub against the bottom of the plates and cause the crustal plates to move.

Map courtesy NOAA

Here are the 7 major plates plus several smaller ones.

Another day we will see how the knowledge you have gained about the interior of the Earth and the plates that make up Earth’s crust helps you understand how some Earth’s landforms are formed.