The above cartoon shows how ocean crust is created at a midocean ridge through volcanic eruption and how the Earth's magnetic field is recorded by the volcanic rock as it cools. The crust is transported laterally away from the spreading center by the process of seafloor spreading (see Oceanus article on paving the seafloor). The geomagnetic field is a dynamic property of the Earth varying on timescales from seconds to millions of years. One of the more unusual properties of the geomagnetic field is it's ability to reverse polarity, so that the magnetic north pole is at the geographic south pole. This reversal in polarity has happened quite often in the past and has been recorded in the rocks of the ocean crust which give rise to variations in our measurements of Earth's magnetic field called "magnetic anomalies". Scientific research on magnetism here in the Geology and Geophysics Department at Woods Hole Oceanographic Institution centers on various aspects of how the magnetism is recorded by the crust, what the magnetic recording can tell us about past history of Earth's tectonic plates and how Earth's magnetic field itself has varied in the past. 

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