Cote I am not arguing the earth is flat, don't know where you got that idea. Yes data is objective, providing the equipment is working correctly. It is our interpretation of it which can vary.
Dating techniques are think are more of a grey area and are not 100% reliably interpretable. I am not certain about the way people claim they are able to interpret dates in the Bible is completely accurate, either. Both would require a great deal of extra study for me, so I remain open minded, which means I do not really hold a firm opinion.
However this does not mean I regard certain views concerning these subjects as unbelievable. From that other perspective, if you put yourselves entirely in their shoes, their views are believable because they believe them.
If you have additional information, I do not think ridicule is particularly helpful either, in this case scenario, if they do genuinely hold what you consider to be outrageous beliefs. It does not help them to learn, only informs them that you have a low opinion of them. Just present the additional information for them to either accept, reject or question.
Yes, sometimes, if we consider a belief to be extremely harmful we must speak out very passionately against it. However often, I do not think the context is urgent enough, to express such high emotion or scorn.