It is based on a story by Don Jakoby who converted it into a screenplay along with David Diamond and David Weissman. The movie was originally written as a serious horror science fiction film, until director Ivan Reitman re-wrote much of the script. A short-lived animated series, Alienators: Evolution Continues, that was loosely based on the film was broadcast months after the movie was released. The film was distributed in North America by DreamWorks and overseas by Columbia Pictures.
Impressed, the two take the science class to survey the meteor site, where the primeval ooze from meteor has rapidly evolved to consist of oxygen-converting fungi and alien flatworms that thrive on the converted atmosphere, with the two scientists taking the flatworms for study. However the military research, led by General Russell Woodman, who Ira worked for five years ago before he was discharged, managed to learn of his finding via tapping his computer and attempt to control the situation to have Allison Reed of the Center for Disease Control continue the research after a 2-week court settlement where Ira and Harry are slapped with a restraining order after Allison reveals the reason for Ira's discharge is that he oversaw a disastrous field test of a new anthrax vaccine that caused debilitating and humiliating side-effects in the test subjects - referred as "Kane Madness."
Once the two find their research findings stolen, they sneak into the military complex disguised as officers to catch a new specimen. However, they discover that the cavern has changed radically in the week they've been absent, now a rain forest-type environment holding a variety of strange anthropodic creatures. But while Ira and Harry are caught when the later is rushed to the camp infirmary after a alien bug forced itself into his suit and him, though Allison is having a change of heart after hearing Ira's reasons. However, the evolving aliens had took advantage of the caverns under Glen Canyon and begin to pop up at the surface, vainly attempting to adapt while attacking any human that crosses their path.
Learning of this from Wayne Grey, a young firefighter trainee who was the first to encounter the meteor, the trio managed to take out a fully-adapted dragon-like pterosaur before heading to the complex to find Woodman meeting with Arizonian Governor Lewis who immediately brings his heavy-handed style of micromanagement to bear on Woodman's operation. After Allison reveals the aliens' incredible growth rate makes them inherently uncontrollable and could over populate the USA in a matter of weeks, Woodman suggests a generous quantity of napalm to solve it.
Though everyone was reluctant to resort to that measure, a attacked by the newly evolved alien primates that attempt to escape convinces the governor to go with the proposal as Allison quits to help Ira solve the crisis with the parcel of primordial ooze he collected, learning that the aliens evolve rapidly when exposed to intense heat, unable to contact Woodman as he refuses to listen to them. By morning, they reach a answer by using selenium, which may be a poisonous to the aliens as arsenic is to carbon-based lifeforms.
Ira's two more under performing students, Deke and Danny Donald, tell the group that selenium is the active ingredient in Head & Shoulders dandruff shampoo. The six of them round up as much Head & Shoulders as they can, load up a fire engine acquired by Wayne, and set out to kill the aliens before Woodman's strike goes ahead. The general, however, begins the strike earlier than planned, forcing a evolutionary response as a alien amoebic life form begin to metamorphose out of control, growing to gigantic proportions while it engulfs the other aliens in the process of surfacing and overwhelming the army before it begins mitosis.
Fortunately, Ira and Harry manages to stop the creature with the selenium before it could asexually reproduce itself, causing the mass to explode raining green glop down for miles around. Later, Governor Lewis holds a press conference as soon as possible, congratulating each member of the heroic party personally (at the same time announcing Wayne's sudden promotion to the fire service as reward for his part). However, Ira and Allison sneak away before he can get to them and make love in the cabin of the fire truck.
|David Duchovny||Colonel (Ret.) Dr. Ira Kane, PhD.|
|Julianne Moore||Dr. Allison Reed, PhD.|
|Orlando Jones||Professor Harry Phineas Block|
|Seann William Scott||Wayne Grey|
|Ted Levine||Brigadier General Russell Woodman|
|Ethan Suplee||Deke Donald|
|Michael Bower||Danny Donald|
|Pat Kilbane||Officer Sam Johnson|
|Ty Burrell||Colonel Flemming|
|Dan Aykroyd||Governor Lewis|
|Gregory Itzin||Barry Cartwright|
|Ashley Clark||Lieutenant Cryer|