Book 12, Question 67
Why Do Magnetic Stripes Decorate Seafloors?
Seafloors have magnetic stripes, like a zebra! Earth's magnetic field flips from time to time. New seafloor records each flip as it forms, like a tape recorder.
More fun facts
- In the 1950s, scientists studied the ocean floor with magnetic tools first built to find submarines in World War II.
- The ocean floor is made of basalt, an iron rich volcanic rock with a strongly magnetic mineral called magnetite.
- When new seafloor rock cools, its magnetite grains lock in the direction of Earth's magnetic field at that time.
- Maps of the seafloor showed a zebra-like pattern of stripes on both sides of the mid-ocean ridges.
- Each stripe has the opposite magnetism of the stripe next to it, one normal and the next reversed.
- This shows that Earth's magnetic field has flipped many times.
- The rock right at the ridge crest always matches today's magnetic field.
- Scientists call the ocean floor a natural tape recording of these flips.
Sources: U.S. Geological Survey
Questions kids ask
Did sailors notice this long ago?
Yes. Sailors from Iceland noticed that the rock could throw off compass readings as early as the late 1700s.