Core motions and the geodynamo

Although the earth's core represents only about one sixth of the earth's mass, it is the origin of a variety of geophysical phenomena. By far the most important is the phenomenon of geomagnetism. It is generally accepted today that the earth's magnetic field is generated by motions in the liquid outer core. The dynamo theory of geomagnetism has become one of the most active areas of mathematical geophysics in recent years. Other phenomena related to motions in the core are the wobble of the earth and the changes in the length of the day that occur on a time scale of the order of a decade. In the following discussion, recent progress in the dynamics of the core and the origin of geomagnetism will be reviewed. In general the attention can be restricted to the past 3 years, since the article by Cox and Cain [1972] has reviewed nearly all the literature through 1971.