Lesson 43: Earth as a Magnet

Key Ideas

• Earth has a magnetic field. It acts somewhat like a giant magnet and helps a compass needle point north.
• Movement of liquid metal deep inside Earth creates most of its magnetic field.
• Magnetic north and true north are not exactly the same direction. The difference depends on where we are.
• Some rocks record Earth’s magnetic field as they form. They show that magnetic north and south have switched many times.
• Earth’s magnetic field redirects many charged particles from the Sun, helping protect our planet.
• Near the poles, charged particles can make gases high in the atmosphere glow. These lights are called auroras.

Vocabulary

• Geodynamo: The process in which moving liquid metal inside Earth creates its magnetic field.
• Declination: The angle between the direction a compass points and true north.
• Paleomagnetism: The study of records of Earth’s past magnetic field preserved in rocks.
• Solar wind: A stream of tiny charged particles flowing from the Sun.
• Aurora: Glowing lights in the sky caused when charged particles interact with gases high in the atmosphere.
• Pole reversal: A change in Earth’s magnetic field in which magnetic north and south switch places.

Discussion Questions

1. If the Earth's magnetic poles drift over time, would an old map's declination reading still be accurate today? What would you check before trusting it?
2. Mars lost its magnetic field and, over time, lost most of its atmosphere. What do you predict would happen to Earth if its core stopped swirling tomorrow?
3. A rock formed a million years ago locks in the field's direction at that moment. What would finding two rock layers with opposite locked-in directions tell you happened between them?

Supplies

• A compass, or the homemade floating-needle compass from an earlier lesson
• A bar magnet, thread, and something to hang it from
• A straight stick, chalk or small markers, and a sunny midday

Slideshow

Videos

Wordwalls