IL PROF. RISPONDE

Paleomagnetic measurement

Paleomagnetism involves measuring the angle of magnetic molecules in rocks.

Magnetic Inclination is the angle that the magnetic needle of the compass dips (points downward) into the earth, measured from horizontal. It is horizontal (0 degrees) at the magnetic equator, and vertical (90 degrees) at the magnetic poles. The inclination is directly dependent on the distance from the poles.

Magnetic Declination is the horizontal angle between the direction to the magnetic pole and the direction to the geographic pole.

If a rock sample (for example a piece of an ancient lava flow) is carefully collected so as to preserve is exact position, it can be placed in a demagnetized chamber, and the precise inclination and declination can be measured for the sample. Together, the inclination and declination tell us exactly where the magnetic north pole was at the time of the formation of the rock (when it cooled enaugh to have the magnetic field freezed within). But note that this is relative to the continental position at the time that the rock was formed. If many measurements are taken from different aged rocks, an apparent polar wandering curve can be constructed which reflects the position of the continent through time as well as the position of the magnetic pole.