ars technica: Nobel Intent - 2010 Mar 02
Nature Geoscience, 2010. DOI: 10.1038/NGEO771Scientists think they have a pretty good idea of how orbital variations drive the glacial cycles that have dominated Earth's recent history. Periodic changes in the Earth's rotational tilt and orientation, called Milankovitch cycles, alter how sunlight gets distributed over the planet's surface, driving the advance and retreat of ice sheets. But some of the details of how this system operates remain a bit hazy, and researchers have been puzzled by a transition called the Mid-Brunhes Event, which took place 430,000 years ago. Before the Mid-Brunhes, even the warm interglacials were colder than the present, with significant ice sheets left behind; afterwards, the conditions were similar to our current ones.