katisara:
Devising new scientific methods depends on a degree 'reasonableness', relying on other scientific beliefs as a baseline. If you expect the answer to be '4 billion years', you are going to automatically toss out any answer which suggests six thousand years. The result is a self-reinforcing, common 'answer' to the question, based on a mix of science and personal bias.
I think you're overstating things here. You make it sound like science only ever gets the answer its expecting, and tosses out anything that disagrees with the accepted answer. You make it sound like the answer that science comes up with is no more valid than any man-on-the-street's opinion. Having worked in science (I'm no longer doing research, but it wasn't too long ago that I was), I can tell you that scientists don't delight in getting the accepted answer, but rather in showing that the accepted answer is wrong. That's what makes you a big name in science: overturning the accepted view. Coming up with results that are consistent with the accepted view helps your career a bit, but if that's all you ever do, you'll just be one of the rank and file, so it's not what people working in science are aiming for.
As hakootoko points out, science didn't expect '4 billion years' to be the answer. When Hutton came up with the idea of (and presented the evidence for) deep time, scientists all expected a few thousand years to be the answer. It was the evidence that led them to the new answer, not their personal biases. And that evidence has been strengthened by look at many different areas, and they all come to more or less the same answer.
Are there some specific examples you're thinking of when you say that scientists 'toss out' answers that suggest 6 thousand years? If so, perhaps we should discuss those, rather than the more general question of whether science is just opinion largely disconnected from facts. I think we won't get much beyond "Is not!" "is too!" unless we talk about specific examples.