One "got ya" question atheists ask Christians is how could their be dinosaurs if the earth is only six thousand years old. Where did all these wondrous creatures come from and then have their bones fossilized in ancient rock layers?
Some Christians believe that there was a gap of millions of years between the first and second verses of Genesis chapter one. Others believe that God put fossils there to make the planet look ancient. Some believe that when the world flooded, Noah couldn't bring such large creatures into the ark. So, what's the real answer?
Hank Hanegraaff, host of The Bible Answer Man, espouses an interesting doctrine which makes logical sense. He teaches that the earth is billions of years old but God used days as a mnemonic device to help ancient people remember the hierarchical order of creation. Viewed this way, it easily explains how light could be created before the stellar bodies. It also matches empirical observations of the universe.
Whenever I've explained this doctrine to fellow Christians, they reacted like I was a horrendous heretic. They cling tenaciously to the six-day creation narrative as if the old earth argument was espousing evolution. This is manifestly untrue. Evolution teaches that there is no divine intelligence and that everything came to be by blind chance. The mnemonic method Moses used when writing the creation account allows for vast periods of geological time but without eliminating God from the picture.
I once believed a lot of notions which I now know are manifestly untrue. Now that I know better, I wrote a book called How I Was Razed so people could learn from my mistakes. Please contact me regarding this wondrous memoir of God's providence. It's well worth reading.