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Why do symmetrical magnetic stripes form on opposite sides of the Mid-Atlantic Ridge?
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geomagnetic field
The magnetic field of a bar magnet has a simple configuration known as a dipole field. Close to Earth's surface this field is a reasonable approximation of the actual field.
The symmetrical magnetic stripes on opposite sides of the Mid-Atlantic Ridge are a direct consequence of seafloor spreading combined with periodic reversals of Earth’s magnetic field.12
The process occurs as follows:
- Crust Formation: Molten magma rises at the ridge’s spreading centre and cools to form new oceanic crust. As the iron-bearing minerals in this cooling rock drop below a specific temperature, they undergo thermoremanent magnetization, locking in the orientation of the Earth's magnetic field at that time.1
- Symmetry through Spreading: As the newly formed crustal slab is continuously split at the ridge, the two halves are pushed in opposite directions away from the centre. Because this happens simultaneously on both sides, the record of the magnetic field is mirrored across the ridge axis.12
- Magnetic Anomalies: When the Earth's magnetic polarity is "normal," the crust records a positive anomaly; when the polarity is reversed, it records a negative anomaly. These alternating stripes of normal and reversed magnetization create the symmetrical pattern observed by geophysicists, providing a permanent record of the history of the seafloor's movement.12