They say to start from the beginning. The Bible almost does that. It starts "in the beginning." That's very close. It then proceeds to say how the world was created in six days, which started a great deal of trouble for Christians, scientists, and Christian scientists.
If you wanted my personal opinion, I'd say that the first chapter of the Bible is apocryphal at best. There is little credible evidence that it was included in the original book of Genesis, and seems to only add unnecessary confusion to a very simple explanation of the origin of the human species. Of course, nobody really wants my personal opinion, so we'll look at the text.
What is a day, exactly? It isn't a twenty-four hour period. According to Jewish tradition (which was the predominant way of thinking among Torah readers at the time), a day spanned from nightfall to the subsequent nightfall, or the time that it takes for the Earth to rotate once about its axis. This would be a handy way to tell what a day is, were it not for the fact that for the first two days, there was no Earth. So where was the light and darkness seen from? Did God uncreate the sun every evening and create it again every morning? That's an explanation, although there's no telling how long that could have taken.
It's possible that God worked very quickly, as creationists believe. Then, from an outside perspective, creation would have only taken 144 hours. However, inside the system of life on our planet, time would have seemed to move at the same slow pace it does now. We have fossil evidence to back up that what was represented as one day took many years from the perspective of the life on Earth. It is possible that if you stepped out of our timestream and walked backwards along our timeline, you would hit the beginning earlier than scientists would have you believe. However, until we intend to step outside of our timestream and start walking backward, such speculation is utterly futile. Technically it's true that we don't know how long Earth's creation actually took, only how long it would have taken assuming that time functioned at the beginning the same way it does now, but if your understanding of Creation is that fish and birds popped into existence one day and then, when they woke up the next morning, there were cattle on the land, then you would be wrong according to empirical evidence as well as what was most likely meant in the Bible. After all, by the time cattle showed up, the seas were "swarming" with fish, for they were "fruitful" and "multiplied." I don't know how much you know about fish, but that generally takes a bit more than what they perceive to be one day.
Most likely, though, the six days were not meant to set up a time frame for creation. The six days were probably just illustration the six phases in which the universe as we knew it came into being. The writer of this chapter probably had no idea how long it actually took. Even assuming it was God, I think He'd have better things to worry about than, knowing how quickly the Earth rotates, how many times it would have rotated in the time in which He was creating it. So why did it say "day"? Well, this concept of the six days of labour followed by one day of rest is echoed in the idea of the Sabbath. It was for the benefit of people who couldn't see the point of taking a day off every week, probably assuming that people wouldn't be stupid enough to assume that generations of aquatic and avian life went by in twenty-four hours.
Another problem with creationism (which isn't so much a literal interpretation of the Bible as they would like to believe, but more of making assumptions based on the Bible and then refusing to admit that those assumptions might be wrong) is that they reject the idea of evolution. I have read a good deal of creationist thought and it seems to me that the main reason they don't believe in evolution is because they don't understand what evolution is. Evolution, in a scientific context, is not the theory that man descended from apes. Apes and humans are similar enough that some postulate that we shared a common ancestor in a time before there were humans or apes, but almost nobody who understands evolution claims that men used to be apes. Evolution is not something specific to human ancestry. It is a way to describe the change in phenotypic ratios in a population, and it is something that definitely happens. When someone dies or is born, that changes the genetic makeup of a population, unless the creatures being born are genetically identical to the ones dying. The changes are often very subtle, especially in a population as large as humanity, and it very rarely creates a new species. It doesn't go in any direction (with some people being more highly evolved than others), and it's quite possible that certain genes go in and out of style and will be present in one generation, then less prevalant in the next, only to return again. That doesn't change the fact that humanity changes in every generation, and we are not the same as we once were, especially if you look at what the Bible actually says.
Evolution, in a broader, less scientific context, as the process of turning one thing into another thing, is not only supported by the Bible, it is the only way that God ever functions. Creation, meaning making something exist that previously didn't, is never demonstrated in the Bible. Staves turn into snakes, water turns into blood or into wine (depending on God's mood), fish turn into more fish, dust turns into people and people turn back into dust or into salt (again, depending on God's mood), but never is something created that wasn't already there at some point. Even on the first day in the Bible, God had a form of matter (what the Greeks referred to as "khaos") with which to work. Read the Bible if you don't believe me. It doesn't say there was nothing. It says the Earth was without form. What God did was mold it into shape, not create it out of nothing.
As for the creation of humans as a species, some would say that the problem with seeing humans as natural creatures is that according to the Bible, Adam was never born. I don't see how they know that Adam really was never born. It said that Adam was created out of earth but, as in Mary Shelley's "Frankenstein," the exact process for creating him was not recorded. There must have been more to it than forming the dirt into a humanoid shape and breathing into its nostrils. If you don't believe me, you can try making your own dirt man and blowing on him and see how far that gets you. So why would the process not involve a birth? It could have been that the image God created of dirt was used to shape the child of some predecessor to humanity. This is supported by Christian mythology. After all, if God created humanity only out of dirt, with no birth involved, then why would He have made Mary pregnant, rather than creating a messiah out of dirt? The birth wasn't mentioned because what made him human was God breathing the soul into him, and before that, there was no humanity, so it wasn't necessary for a very basic understanding of how we became human, but just because it wasn't mentioned that doesn't mean it didn't happen. As for Eve, she could also have been born, perhaps from a union between Adam and another of humanity's predecessors. You see, the genetic material from which Eve was created was taken from Adam's side (or rib), but she could not have been an exact duplicate, because she had two X chromosomes. So where did the rest of the genetic material come from? It could have been from some pre-human creature. After all, it says that a human male came before a human female (or a "suitable helper" - there could have been any number of unsuitable ones), but there were already females of other related species before Adam existed. So Eve was Adam's daughter. Even if you don't believe in the natural birth of Eve, they were still related, for Eve was created from Adam. Either way it's full-on icky. Maybe, though, it's not as bad to fuck your daughter if she's the only thing on the planet that can technically be classified as "human."
Even once there were two humans capable of reproducing, the formation of the human species was not yet complete. Humanity is not today as it was when it was created in God's image. When humans were first created, as close to perfection as God could make, they were naked without shame. The shame for their naked bodies only came after they were corrupted by the forbidden fruit. It was a subtle change, but even in the first generation, humanity had already deviated from God's design. Once outside the Garden of Eden, the Bible talks of the Bnei Elohim - God's children - who interbreed with the humans and change the shape of human life. It never says in the Bible who the Bnei Elohim were. Some say they were angels, but even then, their true nature is not made clear. So what do we know about the products of the union of the Bnei Elohim and human, these grandchildren of God? They were created from a divine image, so they were like humans, but they said to be distinct from humans. If only there was some word to describe something that is like a human - like "hominid" - but I'm just making up gibberish words now.
Of course, this is all conjecture, much like creationism, and there's no solid evidence that it's true. The problem that arises when you have more than one theory on what may be true is the problem of what to teach to children (because, certainly, schools never teach children anything that might not be true). Some creationists say that evolution should not be taught in schools (and some extremists say that creationism should be taught in schools) because we are not sure what the truth actually is. What they don't seem to be taking into account is that the Bible is a historical document designed to tell the story of how humanity came to be in the place it was at the time it was written. It does not contain all of the scientific knowledge behind it. If it did, there would be no need to gather any further information. For instance, penguins are never mentioned in the Bible. Does that mean that penguins don't exist? No, it just means that some things are knowable that aren't in the Bible.
What makes something scientific is not how true it is, it is the method used to gather information. If a science teacher is teaching from the Bible, then he is not doing his job, just as much as if he were teaching from the Magna Carta or the Iliad. Science is not about what has happened, it's about what we know about the world around us. We should be teaching children the scientific method and what information has been gathered using that method. That means teaching what facts support evolutionary and creationist theory.
Scientifically speaking, creationism is about as valid as my own theories of science based on Spider-Man comics. In fact, my theories may be more valid, because we know who wrote Spider-Man. That's not to say that the "God Magic" theory of the origin of life on our planet is untrue, it just isn't something we can state as fact. No matter what you believe in, it doesn't change the duplicable results that scientists can observe. If the crux of the theory you subscribe to is "What we observe happening should not be happening," then it's not a very good theory, and your religious beliefs should not be used to keep the children of this country from getting a proper education.