These include biomagnetism, magnetic fabrics (used as strain indicators in rocks and soils), and environmental magnetism.As early as the 18th century, it was noticed that compass needles deviated near strongly magnetized outcrops.
Magnetic stripes are the result of reversals of the Earth's field and seafloor spreading.
New oceanic crust is magnetized as it forms and then it moves away from the ridge in both directions.
Paleomagnetists led the revival of the continental drift hypothesis and its transformation into plate tectonics.
Apparent polar wander paths provided the first clear geophysical evidence for continental drift, while marine magnetic anomalies did the same for seafloor spreading.
If the magnetization is acquired as the grains are deposited, the result is a depositional detrital remanent magnetization (d DRM); if it is acquired soon after deposition, it is a post-depositional detrital remanent magnetization (p DRM).
In a third process, magnetic grains grow during chemical reactions, and record the direction of the magnetic field at the time of their formation.
The Curie temperature of magnetite, a spinel-group iron oxide, is about 580°C, whereas most basalt and gabbro are completely crystallized at temperatures below 900°C.
Hence, the mineral grains are not rotated physically to align with the Earth's field, but rather they may record the orientation of that field.
The models show a ridge (a) about 5 million years ago (b) about 2 to 3 million years ago and (c) in the present.
Paleomagnetism (or palaeomagnetism in the United Kingdom) is the study of the record of the Earth's magnetic field in rocks, sediment, or archeological materials.
The record so preserved is called a thermoremanent magnetization (TRM).