I have heard many rumors, and questions about this. The most popular one seems to be that Middle-Earth is in fact based on England. I am not what you call learned but I do have the answer.
Middle- Earth is not an imaginary place. It is Europe. The name Middle-Earth comes from the Middle-English term
Middel- erthe which is the name Europeans called their land hundreds of years ago. As Tolkien says in the Prologue to LOTR, those features on his maps do not match those of Modern Europe, because it has changed over time but there's no doubt about a few points of origin.
To answer your other question, Tolkien estimated that Frodo's quest to destroy the ring took place about 6000 years ago, by our calender.
Just a quick fact to finish off; The 'black land' of Mordor is located where you now find the Black Sea.
But I may be wrong
