Sea floor dating
The record so preserved is called a thermoremanent magnetization (TRM).
Because complex oxidation reactions may occur as igneous rocks cool after crystallization, the orientations of the Earth's magnetic field are not always accurately recorded, nor is the record necessarily maintained.
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.
Hematite forms through chemical oxidation reactions of other minerals in the rock including magnetite.
Apparent polar wander paths provided the first clear geophysical evidence for continental drift, while marine magnetic anomalies did the same for seafloor spreading.Although he produced an abundance of circumstantial evidence, his theory met with little acceptance for two reasons: (1) no mechanism for continental drift was known, and (2) there was no way to reconstruct the movements of the continents over time.Keith Runcorn constructed apparent polar wander paths for Europe and North America.Then in 1963, Morley, Vine and Matthews showed that marine magnetic anomalies provided evidence for seafloor spreading.