(View exact match)declinationCATEGORY: term
DEFINITION: The difference between true and magnetic north. In astronomy, the angular distance of a body north or south of the celestial equator.
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paleomagnetismSYNONYMS OR RELATED TERMS: palaeomagnetism, remanent magnetism; paleo-magnetism, palaeo-magnetism; archaeomagnetism
DEFINITION: The magnetic polarization acquired by the minerals in a rock at the time the rock was deposited or solidified. The permanent magnetism in rocks, resulting from the orientation of the Earth's magnetic field at the time of rock formation in a past geological age. It is the source of information for the paleomagnetic studies of polar wandering and continental drift. The field of paleomagnetism involves techniques for determining the age of rocks by analyzing the magnetic field polarity of certain minerals in the rock and its importance in archaeology lies in its use as a dating method. The ancient orientation and intensity of the earth's magnetic field is preserved by the magnetization of iron oxides in rocks and sediments and archaeological materials (archaeomagnetism). Ancient direction and intensity of the earth's magnetic field may be preserved in three ways: a) thermoremanet magnetism (T.R.M.) works through the alignment of the magnetic domains within iron minerals when heated to above the Curie point and subsequently cooling, b) detrital remanent magnetism works through the alignment of clay particles sinking down slowly through still lake or deep ocean water. A block of sediment is magnetized in the direction of the earth's field at the time when it was deposited., and c) sun-dried bricks as the bricks become magnetized in the current direction and intensity of the earth's field. Using igneous rocks, independently dated by potassium/argon, and kilns, hearths, pots etc. dated archaeologically, it has been possible to reconstruct something of the history of the earth's magnetic field. Palaeomagnetism proper is done by studying reversals in the magnetic field of the Earth, the youngest reversal dating to 700,000 bp. Measurement of the declination and inclination of the magnetic poles as it affects materials of different ages can be used to build regional chronologies. Palaeomagnetic dating has also been successfully applied to lacustrine deposits, deep sea cores, and volcanic rocks.