While trying to bury his acorn, Scrat accidentally activates an abandoned alien ship that takes him into deep space, where he unwillingly sends several asteroids en route of collision with Earth. Meanwhile, Manny is worried about the upcoming marriage between Peaches and her fiancé, Julian, while Sid is dumped by his girlfriend, Francine, just as he is about to propose to her. During Manny and Ellie’s wedding anniversary party, some of the asteroids strike the place and the herd barely escape with their lives. Meanwhile at the underground cavern, after stealing a dinossaur egg from a trio of Dromaeosaurs back to its rightful owner, Buck discovers an ancient stone pillar, which he takes to the surface, where he meets Manny and the others.
Buck explains to the herd that according to the pillar, the asteroids had caused several extinctions in the past and with a massive one still incoming, he claims that the only place they could find a clue to stop it is on the site of the impact of the previous ones, as according to its engravings, they always fall at the same place. However, the three Dromaeosaurs, having listened their conversation, decide to stop them, believing that they could be safe from the impact, as they can fly, thus not only getting their revenge on Buck, but also killing all mammals and securing domination over Earth for their species.