In this film, the antics of Scrat the squirrel flying a UFO in outer space, chasing the elusive acorn, ends up inadvertently causing a massive meteor shower to hit Earth. Manny the woly mammoth and his wife Ellie forget, for a moment, their fears that their daughter Peaches will end up leaving them once she gets married to the silly-natured but loveable Julian. They see the fiery rocks hurtling in their vicinity and immediately run for cover, along with their gang of friends (aka The Herd) of many species, eventually running into the spirited and highly intelligent one-eyed weasel named Buck (returning from the third film, Dawn of the Dinosaurs), who concocts a plan to keep the most massive of asteroids from hitting Earth yet again and wiping them all out. Teamwork is employed, but they're going to have to stay a step ahead of a trio of ill-mannered Dino-Birds who want all of these other pesky critters like the dino-egg saving Buck out of the way so they can rule the roost as the most powerful creatures on the newly destroyed planet.