MCCOY: I prescribed sleep.
SPOCK: You prescribed rest, Doctor. The symbols on the obelisk are not words. They are musical notes.
MCCOY: Musical notes? You mean it's nothing but a song?
SPOCK: In a way, yes. Other cultures, among them certain Vulcan offshoots, use musical notes as words. The tones correspond roughly to an alphabet.
MCCOY: Were you able to make sense our of the symbols?
SPOCK: Yes. The obelisk is a marker, just as I thought. It was left by a super-race known as the Preservers. They passed through the galaxy rescuing primitive cultures which were in danger of extinction and seeding them, so to speak, where they could live and grow.
MCCOY: I've always wondered why there were so many humanoids scattered through the galaxy.
SPOCK: So have I. Apparently the Preservers account for a number of them.
MCCOY: That's probably how the planet has survived all these centuries. The Preservers put an asteroid deflector on the planet.
SPOCK: Which has now become defective and is failing to operate.
MCCOY: And we have to find that deflector and put it back into working order, otherwise
SPOCK: Precisely, Doctor.