If you believe Genesis is literally true, it's hard to overcome a 6000-year old universe. There are no gaps in the Genesis geneology. If you want to say there are gaps, you have to admit that Genesis is errant.
Read Genesis 5 and 10. The formula is: A lived X years, and then become the father of B. B lived Y years, and became the father of C...So Adam lived to 130, became the father of Seth. So year 130, Seth is born. Seth lives 105 years, and becomes the father of Enosh. So in year 245, Enosh is born. The math is simple, from Adam to Abraham is about 2000 years. Abraham would have been born about 2000BC. This is calculated from various passages in Genesis and Exodus. That makes Adam's brith about 6000 years ago.
It doesn't seem likely one can get around a 6000-year old antiquity of mankind from Genesis. You could be creative, and say that what is meant is 'Adam lived 130 years, and became the father of some undefined person, who was the great-great-great...grandfather of Seth.' That seems unlikely, but it's probably the only explanation you could come up with. If you do the math, Methusaleh dies the exact year of the flood. Quite a coincidence, if we're talking about 'great-great-great...grandfathers'. Plus, the phrase 'he had other sons and daughters'--this is very odd, if what is being said is 'A became the father of someone who was the great-great-great...grandfather of B, and A had other sons and daughters.'
The antiquity of the universe is a little trickier, but I think you have almost as much difficulty. Yes 'day' is 'yom' in Hebrew, which has more than one meaning...but when the law is given, the Hebrews are instructed to honor the Sabbath day, because God rested on the 7th day. So it doesn't seem to make a lot of sense for them to rest on the 7th day, because God rested on the 7th indefinable period of time. Also, the Genesis formula is 'there was evening and morning, a first day...evening and morning, a second day'...sounds like a 'day' as we understand it today.
And the argument comes back--but how could it be a 24-hour day, when there was no sun on the first few days? The simplest answer, that handles every single difficulty in Genesis--the writer was describing a creation myth. Just like a creation myth that any other culture devised.
I don't know how anyone would reconcile Genesis with modern science, unless you say that it's all mythology. But if you believe the bible is inspired, you run into other problems--like Paul saying that death and judgment passed from Adam to all men. Hard for that to happen, if he's not a historical person.
