Exploratour - The Surface of the Earth
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the National Geographic Data Center/ U.S.G.S.
Sea Floor Spreading
Scientists discovered a curious thing on Earth. If a magnetometer is dragged across the ocean floor, it will measure magnetic polarizations which occur symmetrically on either side of a mid ocean ridge. This phenomena led scientists to speculate that the ocean floor spread apart from a central spreading ridge. As magma came out of the mid-ocean ridge, it became magnetized with the same polarization as the current value of the Earth's magnetic field. Thus the "stripes" of symmetrically occuring magnetic field reveal how fast a particular side of the spreading ridge has spread over time.
In this picture, the mid-ocean ridge in the center of the Atlantic Ocean is shown (the central black line), and on either side, the same magnetic polarizations occur as material of the same age is carried across the ocean floor.
