The Earth's Magnetic Field and Earth's Resources

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1. Key words

2. Inside the Earth

The Earth is made of layers. We live on the thin crust. Under it is the thick mantle of very hot rock. At the centre is the core, which is made mostly of the metals iron and nickel. The outer core is liquid; the inner core is solid because the pressure there is so great.

Remember from magnetism: iron and nickel are magnetic materials. This is the key to why the Earth is magnetic.

3. The Earth's magnetic field

A magnetic field is the area around a magnet where it can push or pull on magnetic materials and on other magnets. The Earth is surrounded by its own magnetic field, and the reason is simple:

The field around the Earth has the same shape as the field around a bar magnet. It is as if a giant bar magnet were placed inside the Earth, along the line from the North Pole to the South Pole.

• A compass needle is a tiny magnet. It turns until it lines up with the Earth's magnetic field, so its north-seeking end (N) points towards the geographic North Pole. This is how people have found their way at sea and in the desert for hundreds of years.
• Look at the diagram: the pole of the 'magnet' near the geographic North Pole is a magnetic south pole. That is why the N end of a compass is pulled towards it — opposite poles attract.
• The magnetic poles are close to, but not exactly at, the geographic poles, and they move slowly over the years.
• The core is extremely hot, much too hot to be an ordinary permanent magnet. Scientists explain the field by the movement of the liquid iron in the outer core. At Stage 8 you only need to say that the core acts as a magnet.
• The field reaches far into space. It protects the Earth from many of the charged particles that stream out from the Sun. Some animals, such as turtles and some birds, use the field to find their way on long journeys.

4. Resources: renewable or non-renewable?

A resource is anything useful that we get from the Earth: fuels for energy, materials for building and making things, water and food. Scientists sort energy resources and materials into two groups.

5. Fossil fuels — non-renewable

Coal formed from the remains of plants that died in swamps millions of years ago. Oil (crude oil) and natural gas formed from tiny sea organisms. They were buried and squashed by layers of rock, and heat and pressure changed them slowly over millions of years. We are using them much faster than they could ever form again, so they are non-renewable.

Problems with fossil fuels: they will run out; burning them releases carbon dioxide, which is changing the Earth's climate; burning coal and oil also releases gases such as sulfur dioxide that cause acid rain; oil spills harm sea life.

How a fossil-fuel power station works: the fuel is burned, the heat boils water, the steam spins a turbine, and the turbine turns a generator, which produces electricity. Wind and tidal power skip the burning: the moving air or water spins the turbine directly.

6. Renewable resources and how we use them

Egypt as an example: Egypt has strong sunshine almost all year, so it has built very large solar farms, such as the one at Benban near Aswan. The coast of the Gulf of Suez is very windy, so wind farms have been built there. The Aswan High Dam produces hydroelectric power from the Nile. The Mediterranean and Red Sea have only small tides, so tidal power is not a good choice for Egypt. The best renewable resource depends on the place.

7. Worked examples

Worked example 1 — Write each resource in the correct column of the table: coal, wind, natural gas, solar, bioplastic, crude oil, tidal, uranium. [3]

1. Ask for each one: will it run out? Wind, sunlight and tides are replaced naturally; bioplastics are made from plants that can be grown again.
2. Coal, natural gas and crude oil are fossil fuels; uranium is a nuclear fuel dug from rocks — all will run out.
3. Marks: all 8 correct = 3 marks; 6–7 correct = 2 marks; 4–5 correct = 1 mark.
4. Common mistake: putting bioplastic under non-renewable because "plastic comes from oil". Ordinary plastic does; bioplastic comes from plants.

Worked example 2 — A compass needle always points north. Explain why. [2]

1. The Earth has a magnetic field because its core acts as a magnet (1).
2. The compass needle is a small magnet, so it lines up with the Earth's magnetic field / is attracted to the magnetic pole near the geographic North Pole (1).
3. Common mistake: writing "the North Pole is made of iron" or "gravity pulls the needle". It is the core, and it is magnetism, not gravity.

Worked example 3 — The table shows where a country gets its electricity.

(a) What percentage of the electricity comes from fossil fuels? [1] (b) What percentage comes from renewable resources? [1] (c) The country wants to use more solar power. Give two reasons why. [2]

1. (a) Fossil fuels are natural gas and oil: 55 + 10 = 65%.
2. (b) Renewables are hydroelectric, wind and solar: 20 + 9 + 6 = 35%. Check: 65 + 35 = 100 ✓.
3. (c) Any two: solar power is renewable / will not run out (1); it releases no carbon dioxide while it generates electricity (1); the fuel (sunlight) is free (1); fossil fuels will run out (1).
4. Exam tip: always check that the parts add up to 100%.

Worked example 4 — A café changes from plastic cups made from crude oil to cups made of bioplastic. Give one advantage and one disadvantage of the bioplastic cups. [2]

1. Advantage (1): made from a renewable resource (plants) / does not use up crude oil / many bioplastics are biodegradable, so they cause less long-lasting litter.
2. Disadvantage (1): growing the plants uses farmland that could grow food / some bioplastics only break down in special composting conditions / they may cost more.
3. Exam tip: "It is better for the environment" is too vague for a mark. Say why: renewable, or biodegradable.

Worked example 5 — Sara says: "Coal is made from plants, and plants grow back, so coal is a renewable fuel." Explain why Sara is wrong. [2]

1. Coal took millions of years to form from buried plants (1).
2. We use it much faster than it can form, so it will run out — it is non-renewable (1).
3. Common mistake: agreeing with Sara. Wood is renewable (trees can be replanted in a few years); coal is not.

Worked example 6 — A town in southern Egypt is far from the sea and has sunshine almost every day. An engineer says tidal power is a good choice for the town. Do you agree? Explain your answer. [2]

1. No (no mark for this alone).
2. Tidal power needs a coast with big tides, but the town is far from the sea (and Egypt's seas have only small tides) (1).
3. Solar power would be a better choice because there is strong sunshine almost every day (1).
4. Exam tip: in "Do you agree?" questions the marks are for the reasons, and the best reasons use the information in the question.

Practice

All pages in this course

Start here

• Stage 8 Science: The Tests and How to Prepare
• Thinking and Working Scientifically: Models, Investigations and Analysing Results

Biology

• Joints and Antagonistic Muscles
• Blood and Its Components
• Breathing, Gas Exchange and Diffusion in the Lungs
• A Balanced Diet, Energy Stores and Lifestyle
• Aerobic Respiration
• Ecosystems, Bioaccumulation and Invasive Species

Chemistry

• The Structure of the Atom
• Purity, Concentration and Chromatography
• Word Equations, Exothermic and Endothermic Reactions
• The Reactivity of Metals
• Impure Products and Solubility of Salts

Physics

• Speed and Distance–Time Graphs
• Balanced and Unbalanced Forces, and Moments
• Pressure, Particles and Diffusion
• Reflection and Refraction
• Dispersion and Colour
• Magnetic Fields and Electromagnets

Earth and space

• The Earth's Magnetic Field and Earth's Resources
• Climate, Weather and Climate Change
• Galaxies and Asteroids

Practice tests

• Stage 8 Science — Practice Test 1
• Stage 8 Science — Practice Test 2
• Stage 8 Science — Practice Test 3