When a meteor bearing single-celled organisms crashes to the Earth, the life forms are initially confined to a cave. Before long the creatures are evolving at an exponentially rapid rate, resulting in fearsome aliens running amok and possibly spelling mankind's doom, or at least the end of man's domination over life on Earth. Investigating the phenomenon is a community college professor, Ira Kane (David Duchovny), his geologist friend Harry Block (Orlando Jones), wannabe fireman Wayne Green (Seann William Scott), and government scientist Allison Reed (Julianne Moore).