Over the last 5 million years, the Earth's glaciers have melted and reformed at fairly regular intervals. The timing is thought to be determined by the amount of solar insolation received at the top of the Earth's atmosphere - a quantity that changes with the position of the Earth in its orbit around the Sun. This motion can be described by three parameters: obliquity (tilt), precession (wobble), and eccentricity (ellipticity). Eccentricity controls the absolute amount of insolation, whereas obliquity and precession control the distribution of insolation on the Earth's surface.

However, the glacial record exhibits times of drastic change, both in the size and frequency of glacial events. Can we determine exactly when these changes occurred? Their abruptness?  Can we differentiate between hypothesized ice sheet models?