---
title: "What's inside the Earth?"
subtitle: "Year 8 Earth and space · Plate tectonics · Lesson 2"
---

# What's inside the Earth?

**Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}}

> **Key question:** The deepest hole ever drilled reached about 12 km. The centre of the Earth is 6371 km down. Everything we know about the rest comes from earthquakes.


:::teacher-note

**In one sentence:** Students describe Earth's layers and their states, explain that temperature and pressure increase with depth, and identify the lithosphere as the rigid outer layer (AC9S8U03, node 1, a hinge node).

**Students should be able to say:** I can name Earth's layers and say whether each is solid or liquid. I can explain that temperature and pressure increase with depth. I can explain that the lithosphere is the rigid outer shell (crust and top of the mantle).

**Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet.

:::


## Engage


:::keep-together

**Under the crust is the mantle, almost 3000 km thick. What do you predict it is like?**

☐ A sea of liquid magma

☐ Ice

☐ Hollow

☐ Solid rock that is so hot it can flow very slowly

My prediction, and why:

{{lines-3}}

:::


:::teacher-note

**What happens:** Solid rock, hot enough to flow very slowly over millions of years, like extremely stiff putty. Only small pockets melt into magma. The only liquid layer is the outer core.

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## Explore

Try it on the board in the tutorial. Was your prediction right? What was different?

{{lines-2}}

## Explain: layers and the lithosphere


:::keep-together

### Solid or liquid

**Solid or liquid?**

Groups: Solid, Liquid

- Crust: {{field-15}}
- Mantle: {{field-15}}
- Outer core: {{field-15}}
- Inner core: {{field-15}}

:::


:::teacher-note

**Answer:** Crust → Solid; Mantle → Solid; Outer core → Liquid; Inner core → Solid

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:::keep-together

### Lithosphere

**What is the lithosphere?**

☐ The crust plus the rigid top of the mantle: Earth's rigid outer shell

☐ Another name for the crust

☐ The core

☐ The liquid layer the plates float on

:::


:::teacher-note

**Answer:** The crust plus the rigid top of the mantle: Earth's rigid outer shell

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:::keep-together

### Deeper

**What happens to temperature and pressure as you go deeper?**

☐ Temperature increases, pressure stays the same

☐ They stay the same

☐ Both increase

☐ Both decrease

:::


:::teacher-note

**Answer:** Both increase

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:::typical

## Elaborate: the skin of an apple


:::keep-together

**If the Earth were an apple, the crust would be about as thick as the apple's skin. What does that tell you?**

☐ The Earth is hollow

☐ The crust is soft

☐ The crust is the thickest layer

☐ The crust is extremely thin compared with the whole Earth

:::


:::teacher-note

**Answer:** The crust is extremely thin compared with the whole Earth

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:::wider

## Elaborate: how do we know?


:::keep-together

**One kind of earthquake wave (S-waves) can't travel through liquids. On the far side of the Earth from a big earthquake, no S-waves arrive. What does that suggest?**

☐ The mantle is liquid

☐ Part of the Earth's interior (the outer core) is liquid

☐ The core is too hot for the waves to pass through

☐ The waves get tired

:::


:::teacher-note

**Answer:** Part of the Earth's interior (the outer core) is liquid

This 'S-wave shadow' is how the liquid outer core was discovered.

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:::


## Evaluate: look back

Write one sentence: "At first I thought… Now I think… because…"

**Revision summary**

- **Crust** (thin, solid) → **mantle** (thick, solid but flows very slowly) → **outer core** (liquid iron and nickel) → **inner core** (solid iron and nickel).
- **Temperature and pressure increase** with depth.
- The **lithosphere** (crust + rigid top of the mantle) is the rigid outer shell, broken into plates; it rests on the soft, slowly flowing **asthenosphere**.

## Exit ticket

:::keep-together

**Name the only liquid layer and explain what the lithosphere is.**

{{lines-3}}

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:::teacher-note

**Answer:** The outer core. The lithosphere is the crust plus the rigid top of the mantle: the rigid outer shell broken into plates.

:::