Earth’s Magnetic Field

Activity Source: 

Science Friday. Adapted with permission.

If you found yourself in the middle of the ocean, do you think you could find your way home? Sea turtles can, thanks in part to Earth’s magnetic field!

All around the surface of the Earth, there is a magnetic field generated by the planet’s large metallic core. The magnetic field varies in strength and direction from place to place, giving different locations unique magnetic “maps.” Sea turtles (and other animals like pigeons, lobsters, and honeybees) can detect and remember patterns in Earth’s magnetic field to find their way over long distances, a behavior called magnetic homing.

How can you navigate like a sea turtle? Find out by making a turtle that can detect magnetic fields and using it to create a magnetic map of its own habitat.


    • Cereal box and a piece of paper
    • Scissors
    • Tape
    • 5-10 refrigerator magnets of varying strengths
    • String
    • Bolt, screw, or nail that is ferromagnetic (sticks to magnets)
    • Modeling clay or play dough
    • Pencil


  1.   Tie a string to a nail or bolt.
  2. Press a small piece of clay onto the bolt, and carefully sculpt it into the shape of a turtle, making sure to keep the bolt on the bottom and the string on the top.
  3. Test your turtle to make sure that it hangs easily and turns towards magnets when you hold it by the string. Watch how it moves when it gets close to and touches a magnet.
  4. Cut a cereal box in half along its longest sides, and tape the corners of one half so it holds its shape when it is set flat on a table. Tape a piece of blank paper to the top of the box and have a friend hide a few magnets of various strengths underneath the box. This is your turtle habitat.
  5. Gently suspend a turtle above the turtle habitat by its string, moving it back and forth until you notice it move in response to one of the magnets. Draw a small dot where you think a magnet is, then draw a larger circle around the entire area where your turtle is able detect the magnet.
  6. When you think you have finished, carefully remove the tape holding the turtle habitat to the table. Lift the turtle habitat up to look at the magnet positions. Compare your map to the positions of the magnet. How similar are they? How would your map differ if your magnets were in different positions?
  7. Search for a magnetic map of a coastline or major ocean. How do the magnetic field lines differ when you compare places along the Atlantic or Pacific coast? What about along the equator compared to the poles? Use the magnetic map you found to answer this question: Where do you think it would be easier for organisms like sea turtles to use magnetic homing, and where might it be harder? Why?

NGSS Connections

  • Science and Engineering Practices — Analyzing and Interpreting Data
  • Disciplinary Core Ideas — Motion and Stability: Forces and Interactions
  • Crosscutting Concepts — Cause and Effect