Only a few Christians need the Earth to be 6000 years old, and that is only to maintain their beliefs in Jesus as being true. If you don't believe in a literal, fundamental Christian type of Jesus, then the age of the Earth doesn't matter. Is Jesus true? Maybe, maybe not. How do the fundy Christians get 6000 years? Ken Ham's
Answers in Genesis site had this article at:
How old is the earth? - Answers in Genesis This is the pertinent quote: Adam was created on day 6, so there were five days before him. If we add up the dates from Adam to Abraham, we get about 2,000 years, using the Masoretic Hebrew text of Genesis 5 and 11.
3 Whether Christian or secular, most scholars would agree that Abraham lived about 2,000 B.C. (4,000 years ago).
Do I care? Do Most Christians care? Do any Jews care? Do people in other religions have alternative views? The answer to the first one is that I do care a little, Jesus might be true. He might be true as believed by Protestant, fundamental, evangelical, born-again Christians. Or, they might be completely wrong and taking it all too literal. Is there proof that they are taking Jesus too literal? Yes, in their extreme literal beliefs of a young Earth, world-wide flood and a 6 day creation.
Good luck Christians on getting people to believe the whole enchilada of your extreme literalism. I know that compromising your beliefs in the Bible undermines your belief in Jesus. But your beliefs in creation undermines other peoples' faith in you as being honest, intelligent and reasonable thinking people. Religion is looked upon as a joke because of you and you are taking Jesus down with you. So, let me ask you, are you sure that the Earth and all of creation is only 6000 years old? Or, is it just a theory?