According to the theory of plate tectonics, the Earth’s crust is broken into many slowly moving plates. Sea floor spreading occurs at the mid-ocean ridge where two plates are moving away from each other. Here, magma rises up from below as the sea floor spreads out to either side as shown in Figure 1. This spreading occurs at about the same rate as your fingernails grow.

The pattern of sea floor spreading can be observed by studying the magnetic field of the rock on the sea floor. At the mid-ocean ridge, magma rises up from the mantle below and cools. As it continues to cool, iron in the rock aligns itself with the magnetic field of the Earth, much like the needle in a compass. When the rock solidifies, this magnetic “signature” is locked in place.

In this experiment, you will use a model of a sea floor spreading zone. The mid-ocean ridge is running north to south down the center of the model. You will use a Magnetic Field Sensor to map the magnetic field of your model and use it to explain how this is evidence of sea floor spreading.


In this experiment, you will

  • Use a Magnetic Field Sensor to measure magnetic field.
  • Map sea floor spreading.
  • Interpret your results.