The structure of the Earth
This Topic is About...
- I will describe a model of the structure of the Earth.
- I will discuss how a model can never be a true copy of the real thing.
You’re going to be a science explorer!
Key Words
- core
- crust
- external structure
- internal structure
- magma
- mantle
Tap to Learn the Meanings!
- core: The very hot, central part of the Earth made mostly of metal.
- crust: The thin, solid outer layer of the Earth that we live on.
- external structure: The outer parts of something, such as the Earth's surface.
- internal structure: The layers and parts inside the Earth.
- magma: Hot, melted rock found under the Earth's surface.
- mantle: The thick layer of hot rock between the crust and the core.
Excellent! You’re learning about Earth’s structure.
What is inside the Earth?
You already know that the outside part of the Earth is made of rocks and sea water. We call this the Earth’s external structure.
But how can scientists find out about the parts of the Earth that are below the surface? These parts make up the Earth’s internal structure. They can’t cut the Earth in half and look at the structure inside. So they have to use a model to show the internal structure.
Remember we often use models in science. Sometimes models help us to understand how something works. Or models can help us to see what something looks like that we can’t see in real life.
To look at the internal structure of the Earth, our model needs to show what the Earth would look like if we could cut it open, like we do with a peach. Here is a whole peach and a peach that has been cut open to see the inside.
FUN QUESTIONS
1. Describe the external structure of a peach.
Show answer
2. Does the right-hand image show the external structure or the internal structure of a peach?
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3. Name the two layers which make up the internal structure of a peach.
Show answer
Here is a diagram to show the internal structure of the Earth.
The structure is made up of different layers: the crust, the mantle and the core.
Crust
The crust is the thin outer layer of the Earth where we live. The crust is formed of rocks. Under the oceans, the crust is about 5 km thick. Under the land, the crust is about 70 km thick. The temperature of the crust increases from 20 °C at the surface to 400 °C at its deepest part.
Mantle
The mantle is about 3000 km deep. Think of a distance that is 3000 km long. This is a much thicker layer than the crust. The rocks in the mantle have been melted by heat. The melted rocks are called magma. The magma can move like a liquid. The temperature rises to 1000 °C.
Core
The core is about 3400 km thick. The core is made up of the metals iron and nickel. The metals in the outer core are liquid.
The inner core is solid because of the pressure of all the other layers. For a long time, scientists thought the temperature of the inner core was 5000 °C. In 2014, scientists used new equipment in a laboratory. They measured the temperature when iron melted under pressure. They found it was 6000 °C — as hot as the surface of the Sun!
Let’s Investigate!
Question: How can we use a model to explain the structure of the Earth?
Scenario: Sofia is trying to explain the structure of the Earth to her friend Zara. She uses a peach as a model of the Earth. Discuss and explore the questions below.
Activity:
- Do you think the whole peach is a good model of the whole Earth? How is it a good or bad model?
- Sofia cuts the peach in half. The cut surface shows the layers inside the peach. As a model of the Earth, which parts of the peach represent the crust, mantle, and core?
- Discuss ways in which the diagram of the inside of the peach is a good model or a bad model of the Earth’s internal structure.
- Read about the internal structure of the Earth again. Find an example of how new information has changed our understanding of the Earth over time.
- Why is it very hot working in a deep mine?
Extension Task:
Explain the internal structure of the Earth to a younger person, such as a brother or sister. Use a model such as a round fruit to help illustrate your explanation.
Tap to See Answers
- 1: The peach is a good model because it shows layers like the Earth. However, it’s not perfect—the materials are very different.
- 2: The peach skin represents the crust, the flesh represents the mantle, and the stone represents the core.
- 3: It’s a good model because it helps visualize layers, but a bad one because the proportions and materials are not accurate.
- 4: Scientists’ understanding of the Earth has improved through studying earthquakes and seismic waves, which show the structure beneath the surface.
- 5: It is very hot in deep mines because temperature increases with depth due to heat from the Earth’s core.
Excellent thinking! You used a simple model to explore a complex structure.
