Learning session 1: The structure of the Earth
The division of the Earth into land, water, and atmosphere is used as a means of approaching a discussion
of its more detailed structure.
The teacher should show images of Earth for the students to see while they are having this discussion. It
could be in the form of a power point or a collection of photographs on the wall. They should represent as
great a variety of environments as possible. Students could use post it notes to write the features onto and
to stick these on the photos of earth’s environments to build up a picture of lots of features of Earth.
Earth. Our planet, our home. It’s very beautiful isn’t it? If I was to ask you to list all of the features that
make up this planet what would you say?
Students co-construct a list of weather features to be shared and discussed.
Earth is made from:
●
Water – salt, fresh, ice, water vapour
●
Land - rocks, dirt, soil, lava, magma
●
Atmosphere – gases, oxygen, carbon dioxide, water vapour
Expand their ideas by questioning.
Water: are there different types of water on Earth? Can water look different in different places?
Land: What do you mean by land? Does all land look the same? Why is it different?
Atmosphere: Would a bird flying in the sky still be on Earth? What do you call that area? How far up does it
go?
We have looked at the surface of the earth – what’s going on inside the Earth? We don’t have the
technology to drill through the centre of the Earth yet so scientists have used indirect evidence to work out
what is going on beneath our feet. One of the big ideas scientists used was density and the other was using
Earthquake waves.
Activity One
Sir Isaac Newton used the information from his studies of the force of gravity to calculate the average
density of the earth. He found it to be more than twice the density of the rocks near the surface. What clues
could this give? (He realised that the interior had to be much denser and so the earth was not hollow)
Experiment: experiment with substances that have differing densities. You could mix them or try to layer
them. You may wish to include heat as a factor. Use substances such as vinegar, molasses, hair conditioner,
oil, water. Jelly. Marshmallow, chocolate drops, custard. Can you make a traffic light jelly in a glass?
Share and discuss
Students should notice how different densities layer themselves. Some will sink while others may float.
Sometimes heating a product changes how it behaves.
Activity Two: Model Earthquake Waves using a slinky spring.
How could earthquakes give us clues to Earth’s interior? Earthquakes send off seismic waves, the behaviour
of these waves could give us clues. This slinky can model the properties of a seismic wave caused by an
earthquake. Explore the different ways it could move. How could we use seismic waves to help discover
Earth’s interior? Experiment with how a slinky moves and see if you can find a connection. You may wish to
try it in water. (Seismic waves from earthquakes come in 2 forms P-waves and S waves. Pushing
compression represents P waves and up and down motion represents S waves. They behave differently in
different mediums)
learning session 1 - the structure of the earth.docx | Page 1
The slinky represents a seismic wave that carries kinetic energy. P-waves (compression waves) travel fastest
through the earth but slower in water. S-waves travel slower and cannot travel through liquids such as
water.
We know from Newton’s interpretations that the deeper you go into Earth interior it becomes increasingly
dense due to pressure. Add to that fact that seismic waves travel faster the denser a material. What would it
mean if the seismic waves travelling through the earth all took longer to travel further and died out in
velocity and strength equally with distance? Scientists who started measuring seismic waves discovered that
some waves travelled with higher velocities even though they had travelled further.
This is because the waves were travelling through different mediums with different densities.
There are areas inside earth with different densities. Why do you think there are different densities and what
could cause this? Could you now predict the types of seismic waves that would propagate under different
circumstances after travelling across different areas
Activity
Design a model or drawing of Earth’s interior that could account for these discrepancies.
Some are solid and other could be in liquid form. That these areas could be made of different materials. The
change from solid to liquid may be due to heat.
How could we find out what materials are there? maybe … the insides sometimes come out at the surface,
and if so where could we see that?
Encourage the students to think about volcanoes and lava - they may also mention underground water and
gases. We can refer back to these later.
If lava comes out from the inside of Earth what does that tells us? You are right! The inside of Earth is very
hot, in fact it's so hot that it melts rock and metal! What might cause it to be hot?
Encourage students to consider friction, pressure.
Let's look at what’s inside planet Earth. Using a small can of fruit, jelly (cool but unset) and ice cream; mix
these three ingredients in a class bowl – you should see the three layers separate out due to their different
densities.
The teacher should draw a diagram with the three main layers of the earth; the densest core, the mantle
and the crust – the diagrams below are a guide only.
learning session 1 - the structure of the earth.docx | Page 2
The Earth is a bit like a peach with the stone as its centre, but instead of a stone Earth has a solid ball of
iron and nickel. Surrounding this ball is an extremely hot area of melted metal that is slowly moving around
the solid centre. Next is a massive area of melted rock. Who knows what melted rock is called? (Magma)
Next comes the crust which is a bit like the skin of the peach, it is very thin compared to the whole of the
Earth. We live here, on the crust.
Watch this clip.
See Earth’s Layers.
Activity choices
●
Develop an experiment that explores different densities of properties and how they behave.
●
Design a measurement device or method for measuring density.
●
Create a device that could measure seismic waves. http://makeprojects.com/Project/EarthquakeDetector/488/1
●
Watch a documentary and report back to the class.
>
http://topdocumentaryfilms.com/inside-planet-earth/
>
http://topdocumentaryfilms.com/magnetic-storm/
●
Gravity is a force that pulls towards the centre of the Earth – if you were falling through to the centre of
the earth what would happen to you and why?
●
Design a vehicle that could with stand the environment at the centre of the earth – outline why you
have included the features on your vehicle.
learning session 1 - the structure of the earth.docx | Page 3