Twenty thousand years ago, Earth was a wondrous, prehistoric world filled with great danger, not the least of which was the beginning of the Ice Age. This animated feature revolves around sub-zero heroes: a woolly mammoth (voiced by Ray Romano), a saber-toothed tiger (Denis Leary), a sloth (John Leguizamo), and a prehistoric combination of a squirrel and rat, known as Scrat (Chris Wedge). To avoid really bad frostbite and save a lost human infant, the planet's creatures begin migrating south. Before the mission is complete, they brave a lava pit, caverns of ice, and a traitorous plot within their midst.