Nigel Kneale's Quatermass TV series spawned a brief film series produced over an eleven-year period; 1967's Quatermass and the Pit, released in the US as Five Million Years to Earth, was the third and (until 1979's Quatermass Conclusion) last of the features. As with previous chapters in the Kneale saga, the film begins with a baffling scientific discovery. This time it's an alien ship, alive after 5,000,000 years, discovered during the excavation of a new subway line. The craft is able to cause psychic disturbances in individuals genetically connected to the machine; it also prompts them to see dead Martians as ghostly entitites nearby. In time, conclusions drawn from these events lead scientists to shocking conclusions about the origins of the human race.
by Hal Erickson synopsis