The Gyricity of the Earth*

An introductory exploration of the mechanical influence of long-term gyricity or gyroscopic effect on the dynamics of the Earth is presented. Gyricity exists in a deformable, energy-dissipating, and thus rotationally unstable Earth in the form of internal torques, or the rate of change of angular momentum independent of external torques. The kinematics of the internal torques appear compatible with the gross features of the Earth’s surface plate tectonics. The internal torques calculated bases on present observations do not balance with each other, but their secular components are all of the order of 1023 erg. Based on the history of polar excitation, the equation -of secular motion in the Earth in the absence of external torques is derived under the law of conservation of angular momentum. The equation links the dynamics of polar instability with those of secular motions, notably plate motion and mantle flow, in the Earth. Gyricity is found to dominate the driving mechanism of the secular motions.