Paleomagnetic field / Paleomagnetism
Paleomagnetic field (Paleofield) means the ancient geomagnetic field
The origin of the geomagnetic field is electro-magnetic physical processes in the Earth's outer core. In the outer core, liquid metal is drastically convecting and the flow is always changing. Therefore, the magnetic field induced is also countinuously changing. The geomagnetic field a dicade ago, a hundred year ago, a million years ago, ..., were not same as the present field. These ancient fields are called paleomagnetic field.
We cannot imagine a paleomagnetic field only fron the observation of the present field. However we have a powerful method for obtaining paleofield, that is to measure the fossil of the a geomagnetic field printed in a rock formed in the past. Almost all rocks include very fine crystals of magnetic minerals such as magnetite. These natual magnets made align parallel to the geomagnetic field when they were formed such as volccanic rocks erupted from the volcanos and sedimentary rocks precipitated on the ocean bottom. So, we can obtain the direction and intensity of paleofield at the rock formation by measuring the magnet in the laboratory.
Paleomagnetism) is a kind of academic study researching the paleomagnetic field by measuring the rocks in the outcrops. Paleomagnetism is used for application of the various studies in the Earth and planetary sciences. For example paleomagnetic results were most effective evicences for the constructing continental drift theory and plate tectonics in 1950s and 60s