Evolution of the obliquity and the angle ﹩\psi +{\rm{\Omega }}﹩ (left) for the Earth-mass planet at point h in Figure 13, and the power spectra of the inclination and obliquity variables (right). Vertical dashed lines represent the minimum and maximum axial precession rates, which vary with obliquity. The broad peak of the obliquity variables is indicative of chaotic motion.