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How do iron-bearing minerals preserve the direction of Earth’s ancient magnetic field?
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paleogeography
Watch a time-lapse of Earth changing through geologic time, from the Cambrian Era to the projected period of Pangea Proxima.
Iron-bearing minerals preserve the orientation of Earth’s ancient magnetic field through a process known as remanent magnetism. This permanent record is primarily formed in two ways:
- Igneous Rocks: As molten rock cools, magnetic minerals pass through the Curie point. At this stage, the magnetic domains within the minerals align themselves with the Earth’s magnetic field, effectively locking in its orientation as the rock solidifies.12
- Sedimentary Rocks: During deposition, small grains of magnetic minerals settle into a sedimentary matrix. These grains orient themselves according to the Earth’s magnetic field before the sediment undergoes final consolidation and lithification.12
Because the Earth’s magnetic field lines are parallel to the surface at the Equator and vertical at the poles, the dip of these minerals provides a record of the latitude at which the rock formed. This data is essential for paleogeography, as it allows scientists to reconstruct the past latitudinal positions of continents and track their movement over geologic time.23