Composition of the Earth

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Lesson notes

Earth's Layers

The Earth is roughly spherical and consists of four layers: **crust**, **mantle**, **outer core**, and **inner core**.
The **crust** is the thinnest layer, 6–70 km thick, made of rock, and divided into **tectonic plates**.
The **mantle** is ~3000 km thick, made of mostly solid rock that flows slowly; **convection currents** here move tectonic plates.
The **outer core** is a liquid layer ~2000 km thick, primarily **iron and nickel**, responsible for Earth's **magnetic field**.
The **inner core** has a radius of ~1400 km, is the hottest layer at ~6000 °C, but is **solid** due to immense pressure.
Temperature generally **increases with depth**.

Composition of the Crust

Most abundant element in Earth's crust: **oxygen (46%)**.
Second most abundant: **silicon (28%)**.
Third: **aluminium (8%)**.
Fourth: **iron (6%)**.

Cross-section of Earth showing the four layers: crust, mantle, outer core, inner core.

Slides

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Practice questions

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1.What is the layer at the centre of the Earth?
Easy
- AInner core
- BOuter core
- CMantle
- DCrust
2.Which layer of the Earth is the thickest?
Easy
- AMantle
- BCrust
- COuter core
- DInner core
3.What is the approximate thickness of the crust?
Easy
- A6 to 70 km
- B3000 km
- C2000 km
- D1400 km
4.Which layer of the Earth is the hottest?
Easy
- AInner core
- BOuter core
- CMantle
- DCrust
5.What is the most abundant element in the Earth's crust?
Easy
- AOxygen
- BSilicon
- CAluminium
- DIron
6.What is responsible for the Earth's magnetic field?
Medium
- AThe outer core
- BThe inner core
- CThe mantle
- DThe crust
7.What are the different parts that the crust is divided into?
Medium
- ATectonic plates
- BConvection currents
- CContinents
- DLayers
8.What do convection currents in the mantle lead to?
Medium
- AMovement of tectonic plates
- BEarth's magnetic field
- CFormation of the crust
- DHeating of the core

Revision notes

## Composition of the Earth The Earth is roughly spherical and consists of four layers: - **Crust**: The thinnest layer (6–70 km thick). Made of rock. Divided into tectonic plates. - **Mantle**: ~3000 km thick. Mostly solid rock that flows slowly. Convection currents here move tectonic plates. - **Outer core**: 2000 km thick, liquid, made of iron and nickel. Responsible for Earth's magnetic field. - **Inner core**: 1400 km radius, hottest layer at 6000°C, but solid due to high pressure. Temperature increases with depth. ### Most abundant elements in Earth's crust: 1. Oxygen (46%) 2. Silicon (28%) 3. Aluminium (8%) 4. Iron (6%)

Crust: The thinnest layer of the Earth at 6 to 70 km thick, made of rock, divided into tectonic plates.
Mantle: The layer below the crust, around 3000 km thick, made of mostly solid rock that flows slowly over time.
Outer core: A liquid layer below the mantle, 2000 km thick, primarily made of iron and nickel, responsible for Earth's magnetic field.
Inner core: The centre of the Earth, 1400 km radius, hottest layer at 6000°C, solid due to high pressure.
Tectonic plates: Different parts that the crust is divided into.
Convection currents: Currents in the mantle that slowly move the tectonic plates.

Flashcards

What are the four layers of the Earth?

Crust, mantle, outer core, inner core.

What is the thinnest layer of the Earth?

The crust, which is 6 to 70 km thick.

What is the thickest layer of the Earth?

The mantle, which is around 3000 km thick.

What is the outer core made of?

Primarily iron and nickel.

What is the inner core made of?

Primarily iron and nickel, but solid.

What is the temperature of the inner core?

6000 °C, the hottest layer.

Why is the inner core solid despite high temperature?

Because it experiences more pressure than the other layers.

What is responsible for the Earth's magnetic field?

The outer core, which is liquid and made of iron and nickel.

What are tectonic plates?

The different parts that the crust is divided into.

What causes tectonic plates to move?

Convection currents in the mantle.

What is the mantle made of?

Mostly solid rock that flows slowly over time.

How does temperature change with depth in the Earth?

Generally, temperature increases with depth.

What is the most abundant element in the Earth's crust?

Oxygen (46%).

What is the second most abundant element in the Earth's crust?

Silicon (28%).

What is the third most abundant element in the Earth's crust?

Aluminium (8%).

What is the fourth most abundant element in the Earth's crust?

Iron (6%).

What is the crust made of?

Rock.

What is the thickness of the outer core?

2000 km.

What is the radius of the inner core?

1400 km.

What is the state of the outer core?

Liquid.

What is the state of the inner core?

Solid.

What is the state of the mantle?

Mostly solid rock that flows slowly.

Name the layers of the Earth from outermost to innermost.

Crust, mantle, outer core, inner core.

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