2001: A Space Odyssey is a film about mankind's continual self-overcoming through technological and scientific achievements. Though the film spans millennia, a mysterious black monolith reappears during each of the film's four major parts, at every threshold of mankind's progress: the invention of bone tools, the discovery of evidence for extraterrestrial life, the defeat of man's most advanced tool, the evil HAL 9000 supercomputer, and man's rebirth after overcoming space and time. The film is notable for its revolutionary use of special effects, color, long takes and montage, and sound.