Competitive Exams: Paleomagnetism

It refers to the preservation of magnetic properties in the older rocks of the earth. It gets magnetized depending on the presence of iron content in the rock and is preserved frozen at temperature below Curie point, which is generally 600 degree C.

• The direction and inclination of. The magnetic field of rocks of different ages have been measured from rock samples collected from all. Over the world, and this information can be used to as certain the location of the Earth's magnetic pole at the time when those rocks were formed. The direction of the magnetic field of a given rock sample indicates the direction in which the magnetic pole of the Earth lay when the rock formed, while the inclination of the magnetic field of the rock indicates how far away from the collection site the magnetic pole was located. For example, if the inclination of the magnetic field is nearly horizontal, the magnetic pole of the Earth must have been 90 great circle degrees away from the collection site because the site was near the magnetic equator. On the other hand, if the inclination of the magnetic field of a rock is vertical, the collection site would have been located at or near the Earth's magnetic pole at the time of rock formation. It is assumed that if enough rock samples of a given age are averaged together, the average position of the magnetic pole will be the same as the average position of the Earth's rotational pole. Thus, paleomagnetic poles provide the location of the planet's rotational pole.

• The geocentric axial di-pole magnetic field represents 95 per cent of earth's total magnetism. Global system of Lithosphere plates: Depending upon the intensity of boundary activity plates are divided into greater plates, lesser plates and sub-plates. Greater plates-Pacific, American (N and S), European (having Persian sub-plate), African (having Somalia sub-plate), Australian-Indian and Antarctic plates.

Lesser plates

• Nazca, Cocos, Philippines, Caribbean, Arabian, Juan de Fucca, Caroline, Bismark, Scotia plates. Movement of Plates

• Constantly in motion with respect to each other and to Earth's axis of rotation. Plate velocity varies all along the sphere of the Earth.