Young Earth Creationism is an opinion held by some Christians, but it isn’t necessary to the Christian faith. The world can be billions of years old, and Adam and Eve could even be billions of years old, and the essentials of Christianity aren’t really affected by that idea. All we are required to believe about the Creation is that, God created everything that is, both seen and unseen, and that Adam and Eve had no human ancestors, and they are the ancestors of every human being who has ever lived. If evolution is true, it seems less likely that a whole crowd of humans just suddenly popped up out of nowhere, but if two of them appeared, and they happened to live in the same place at the same time, so that they were able to reproduce, then there you have the human race.