The black & white footage shown to Julian Rome is footage from The Thing from Another World (1951). This footage was also used in the remake of The Thing from Another World, John Carpenter's The Thing (1982), and it is the film that R.J. MacReady finds in the destroyed Norwegian camp.
The hallways of the underground base were made out of paper and plastic.
The alien found inside the pod is the same one from the film 'Independence Day' (1996)
The CGI effects featured at the climax took six months to do.
The corn in the cornfield was made out of paper.