(pÄ'lÄ-Å-mÄg'nÄ­-tÄ­z'Ém) The fixed orientation of a rock's magnetic minerals as originally aligned at the time of the rock's formation. Paleomagnetism is usually the result of thermoremanent magnetization (magnetization that occurs in igneous rocks as they cool). Examination of the paleomagnetism of the Earth's ocean floors revolutionized the field of geology by providing evidence for the existence and movement of tectonic plates. See Note at magnetic reversal.