Using a modified form of Weertman's (1976) model, predictions of ice age continental ice sheet growth and decay are made for the past 550,000 years by using Vernekar's (1972) insolation anomaly data. While forcing is at periods near 19,000, 23,000, and 41,000 years, model response consistently predicts dominant long-period responses, most commonly at 100,000 and/or 400,000 years, in addition to significant responses at the forcing periods. The model response lends support to the hypothesis of Hays et al. (1976) that nonlinear response of the earth system to fluctuations of the orbital parameters is responsible for the long-period climate fluctuations recorded in deep-sea cores.