Re: Movie :2010
The monolith on Europa was there to protect and guide the Native Europaians, just as a monolith had done for the human race millions of years earlier.
I figured the one on the Moon was the same one that guided early man (Since no sign of it had been found on the Earth). I figured it went to the Moon when it was no longer needed to guide the human race. I got the impression that its purpose there was to alert its creators that the human race was space faring.
I have read all 4 books and saw the two movies.