Was Melchizedek Born on Earth?
Was Melchizedek a being from another "world" brought here to deliver the keys to the priesthood?
Abraham lived at the time of Melchizedek. Abraham chapter 1 tells us that he (Abraham) received his priesthood through the fathers; back to Adam. So the priesthood was already upon the earth and didn't require a person from another planet. Priesthood can't be passed on without the appropriate keys to know how and when to use the priesthood. So the keys were here also.