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How do rocks on the ocean floor provide evidence for geomagnetic reversals?

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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.

Oceanic crust provides evidence for geomagnetic reversals through the permanent record of Earth's magnetic field preserved in rocks as they form at spreading centres.1

As molten rock cools, iron-titanium oxide minerals undergo thermoremanent magnetization, locking in the orientation of the magnetic field present at that time. Because seafloor spreading continuously creates new crust at ridge crests, this crust acts as a conveyor belt, moving away from the center and carrying a chronological record of the field's polarity.12

When the magnetic field is in its "normal" state, the crust exhibits positive magnetic anomalies; when the field is reversed, it exhibits negative anomalies. These anomalies appear as parallel, symmetrical patterns on both sides of oceanic ridges. By mapping these patterns, scientists can correlate the magnetic signatures with known time scales of past reversals, allowing them to date the seafloor and reconstruct the history of ocean basins.1