This is a REALLY funny film about Community college professor Ira Kane who is invited by geology teacher/girls' volleyball coach Harry Block to investigate a meteor that has crashed into a network of underground caverns under the sleepy Arizona town of Glen Canyon. When they get to the site of the crash and they try to take a sample they find some blue ooze coming out of the meteor and when they bring the sample back to the college and Ira finds the ooze has single-celled nitrogen-based organisms and he goes to tell Harry and by the time they get back they've evolved into multi-celled organisms. The aliens are evolving from flatworms to bugs, mammals and dinosaurs and Ira, Harry and young trainee firefighter Wayne (who saw the meteor crash) have to kill an oxygen-tolerant dragon alien in a shopping mall. Here's when they kill it.
And here's the trailer for the film.