Cambridge Lower Secondary CheckpointStage 8

Earth and Space: Earth in space

Science Stage 8 Chapter Notes

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Earth and Space: Earth in space
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In this chapter

  1. 1The Earth as a Giant Magnet
  2. 2Magnetic vs. Geographic Poles
  3. 3Introduction to Asteroids
  4. 4Asteroid Impacts on Earth

1. The Earth as a Giant Magnet

The Earth has a magnetic field that extends from its interior out into space, where it meets the solar wind. This field is generated by the movement of molten iron in the Earth's outer core. This process, known as the dynamo effect, creates electrical currents which in turn produce the magnetic field. This field acts like a protective shield, called the magnetosphere, deflecting most of the charged particles from the Sun. Without it, the solar wind would strip away our atmosphere.

Key term

Magnetosphere: The region of space surrounding Earth where the planet's magnetic field is dominant and deflects the solar wind.

Examiner insight

Examiners reward answers that correctly and specifically link the molten outer core to the generation of the magnetic field.

Fun fact

The Earth's magnetic field protects our atmosphere from being stripped away by the solar wind, which is what scientists believe happened to Mars, leaving it a cold, barren planet.

Worked example 12 marks

a) What part of the Earth's structure causes its magnetic field? [1]b) Name the primary metal that makes up this part. [1]

  1. 1

    a) The magnetic field is generated in the outer core.

  2. 2

    b) The outer core is primarily composed of molten iron.

Recap

  • The Earth behaves like a giant bar magnet.
  • Its magnetic field is created by the movement of molten iron in the outer core.
  • This field creates a protective shield called the magnetosphere.
  • The magnetosphere protects Earth from harmful charged particles from the Sun.
  • The process of generating the field is called the dynamo effect.

Quick check

  1. What is the name of the protective shield created by Earth's magnetic field?1 mark
  2. What two elements is the Earth's core mostly made of?1 mark

2. Magnetic vs. Geographic Poles

It's important to distinguish between the Earth's two types of north and south poles. The Geographic Poles are the points where the Earth's axis of rotation meets the surface. The Magnetic Poles are the points where the magnetic field is strongest. A compass works because its magnetic needle aligns with the Earth's magnetic field lines. The 'north' end of the compass needle is a magnetic north pole. Since opposites attract, it is attracted to a magnetic south pole. This means the Earth's 'Magnetic North Pole' (the place a compass points to) is actually a magnetic south pole!

Key term

Geographic North Pole: The point in the Northern Hemisphere where the Earth's axis of rotation intersects its surface.

Common pitfall

A common mistake is to think the Geographic North Pole and the Magnetic North Pole are the same. They are in different locations and the Magnetic North Pole moves over time.

Fun fact

The Earth's magnetic poles are not fixed. The North Magnetic Pole is currently moving from the Canadian Arctic towards Siberia at a speed of about 55 km per year.

Worked example 13 marks

A bar magnet is allowed to rotate freely on a string. Explain which pole of the bar magnet will point towards the Earth's Geographic North Pole and why.

  1. 1

    The north pole of the bar magnet will point towards the Earth's Geographic North Pole.

  2. 2

    This is because the Earth's magnetic pole located near the Geographic North Pole is actually a magnetic south pole.

  3. 3

    Opposite magnetic poles attract, so the north pole of the magnet is attracted to the Earth's magnetic south pole.

Recap

  • The Geographic Poles are based on the Earth's spin axis.
  • The Magnetic Poles are based on the Earth's magnetic field.
  • The Geographic and Magnetic Poles are not in the same location.
  • A compass needle points to the Magnetic North Pole.
  • The Earth's Magnetic North Pole is technically a magnetic south pole.

Quick check

  1. Does a compass point to the Geographic North Pole or the Magnetic North Pole?1 mark

3. Introduction to Asteroids

Asteroids are large, irregularly shaped rocks that orbit the Sun. They are sometimes called minor planets. Scientists believe they are the rocky remnants left over from the formation of our Solar System about 4.6 billion years ago. Most asteroids are found in a vast ring between the orbits of Mars and Jupiter. This region is known as the main Asteroid Belt. While planets are large and spherical due to their gravity, asteroids are much smaller and have not 'cleared' their orbit of other debris.

Key term

Asteroid Belt: The region of the Solar System located roughly between the orbits of the planets Mars and Jupiter, where most asteroids are found.

Examiner insight

To earn marks, students should be able to state at least two clear differences between asteroids and planets, focusing on size, shape, or orbital characteristics.

Worked example 12 marks

State two features of asteroids that make them different from planets.

  1. 1
    1. Asteroids are much smaller than planets.
  2. 2
    1. Asteroids are typically irregularly shaped, whereas planets are spherical.
  3. 3
    1. Asteroids have not cleared their orbital path of other objects, which is part of the definition of a planet.

Recap

  • Asteroids are rocky objects that orbit the Sun.
  • They are leftover material from the formation of the Solar System.
  • Most asteroids are located in the Asteroid Belt between Mars and Jupiter.
  • Asteroids are smaller and more irregularly shaped than planets.
  • They are not large enough to have cleared their orbits.

Quick check

  1. Where in the Solar System is the main Asteroid Belt found?1 mark
  2. What are asteroids believed to be made from?1 mark

4. Asteroid Impacts on Earth

While most asteroids remain in the Asteroid Belt, some have orbits that bring them close to Earth. These are known as Near-Earth Asteroids. An impact can occur for two main reasons: firstly, the asteroid's orbit might cross Earth's orbit, and secondly, Earth's strong gravitational pull can capture a passing asteroid and pull it towards the surface. Small asteroids impact Earth's atmosphere frequently, burning up as meteors or 'shooting stars'. Large impacts are much rarer but can have catastrophic consequences. Evidence of past large impacts can be seen as impact craters on the Earth's surface.

Key term

Impact Crater: A circular depression in the surface of a planet or moon formed by the high-velocity impact of a smaller body.

Common pitfall

Confusing meteors, meteoroids, and meteorites. A meteoroid is the rock in space, a meteor is the streak of light as it burns in the atmosphere, and a meteorite is any part that survives to hit the ground.

Fun fact

The Chicxulub crater, buried under Mexico's Yucatán Peninsula, is from the asteroid impact 66 million years ago that is widely blamed for the extinction of the dinosaurs.

Worked example 12 marks

Explain two reasons why asteroids sometimes collide with Earth.

  1. 1
    1. Some asteroids have elliptical orbits that cross the path of Earth's orbit around the Sun, creating a chance for collision.
  2. 2
    1. The Earth exerts a strong gravitational force on nearby objects, which can pull a passing asteroid out of its original path and onto a collision course.

Recap

  • Some asteroids have orbits that cross Earth's path.
  • Earth's gravity can pull in passing asteroids.
  • Small asteroids burn up in our atmosphere, creating meteors.
  • Large impacts are rare but can cause significant damage and climate change.
  • Impact craters are the geological evidence of past asteroid collisions.

Quick check

  1. What is the name for a crater left by an asteroid collision?1 mark

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. What part of the Earth is responsible for generating its magnetic field, and what is this part primarily made of?2 marks
  2. Define the term 'asteroid' and state where the majority of them are found in our Solar System.2 marks
  3. A hiker is using a standard magnetic compass. Explain in detail why the compass needle points towards the geographic north.3 marks
  4. State two distinct ways in which asteroids are different from planets.2 marks
  5. Explain the two main reasons why an asteroid might collide with Earth.2 marks
  6. The Earth's magnetic north pole is known to be moving. Explain why this is not a major problem for a person navigating a single-day journey, but might be for creating maps intended to last for decades.3 marks
  7. Describe the origin of asteroids and explain what the 'Asteroid Belt' is.3 marks
  8. Draw a simple diagram of the Earth. Sketch at least four magnetic field lines around it, using arrows to show the direction of the field. Label the Geographic North Pole and the approximate location of the Magnetic North Pole.4 marks
  9. The Moon's surface is covered in impact craters, but very few are visible on Earth. Suggest two reasons for this difference.2 marks
  10. What is the name of the protective region of space around Earth created by its magnetic field, and what does it protect us from?2 marks

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