Kaily:
What you are referring to is known as Young Earth Creationism (YEC.) Many of the more fundamental protestant faiths believe this as they believe the Bible is literal and as such is not open to interpretation.
What many do not realize is that we are reading an imperfect translation which is why we need Tradition to help us interpret. In the original languages in which the Bible was written (in this case as we are talking Genesis it would be Hebrew) there was actually no word for a 24 hour day. That concept did not exist at that time. Instead, the word used simply meant “a closed ended period of time.” This means that period of time could indeed be one 24 hour day as it has been translated in modern Bibles, or it could be thousands or even millions of years.
When I was Southern Baptist, I even had a Sunday School teacher who said that “wouldn’t it be funny if God put a bunch of bones in the ground just to see what we would do with it?” I do not agree with YEC or a literal interpretation of the Bible (part of the reason I converted). But it can be very fascinating to read about, and at one point when I was Baptist I even had a book that explained the YEC view. I wish I could remember where it was because it can certainly help clarify some of the beliefs, and it did make for interesting reading even if I didn’t agree with it.