Why is the age of the earth such a controversial topic?
If I got the idea right this is a question that probably will fall into the philosophical/religious field...I think!
I am an amateur astronomer and also collector of fossils.
One time when I was reading about dating (meteors or fossils) I came across this:
Archbishop James Ussher (Bishop in the Church of Ireland, from 1625 to 1656) took the genealogies of Genesis, assuming they were complete, and calculated all the years to arrive at a date for the creation of the earth on Sunday, October 23, 4004 B.C.
I was puzzled more about the precision (23rd???) than the amount or length of time.
Actually he was very ingenious and used a really interesting method to get this result evaluating the most probable length of the life of the various patriarchs (in the Bible) and considering a fixed length for the year.
On the other hand we have radioactive decay and radioactive dating that give us a different picture placing some of the rocks on Earth in the billion year range of age!
So the controversy comes from the fact that we have a problem here. Also because this kind of problems tends to divide the supporters of one or other opinion in two separate factions that, exactly as football supporters of opposing teams, cannot accept each others,
I humbly consider myself a scientist and think that actually Bishop Ussher behaved as a scientist as well!!!
Bishop Ussher devised a very nice and neat theory based upon research (from literature and documents), mathematical methods and observation! Ok, it is wrong, we know that, but who cares! It is very intriguing and, as all the theories, fascinating! It has nothing to do with beliefs or being religious or a scientist....it is a theory!
Exactly as in a football game, the Bishop's team lost the game but the game was very good, they played very well and had 2 or 3 good shots on goal !!!