Usually, even a non-Christian knows something about the earth, the heavens, and the other elements of this world, about the motion and orbit of the stars and even their size and relative positions, about the predictable eclipses of the sun and moon, the cycles of the years and the seasons, about the kinds of animals, shrubs, stones, and so forth, and this knowledge he holds to as being certain from reason and experience. Now, it is a disgraceful and dangerous thing for an infidel to hear a Christian, presumably giving the meaning of Holy Scripture, talking nonsense on these topics; and we should take all means to prevent such an embarrassing situation, in which people show up vast ignorance in a Christian and laugh it to scorn.
--Augustine, The Literal Meaning of Genesis, translated by John Hammond Taylor
St. Augustine made that comment in the early 400s AD, about 1450 years before Darwin's On The Origin Of Species, and went on at some length in that vein. The idea that the account in Genesis recounts the Earth's natural history in a simple way is an old one, but it was rarely taken seriously until recent centuries. This is why when Augustine wanted to explain how to take Genesis literally, he wrote a 400-page work on the topic, not a pamphlet that said it's all simple. (I have not read this work yet; I just found out about it and ordered it while researching for this post.)
I think the straightforward natural history reading of Genesis was largely invented recently as a reaction to the medieval Roman Catholic church. At one time, when the Church was a career, social, and political organization, they strongly discouraged Bible reading, including forbidding the translation of the Bible to "vulgar tongues", e.g. not Latin; and they held that all Bible interpretation was a matter of complex allegorical interpretation only to be undertaken by Church professionals. This helped keep people away from finding out inconvenient doctrines like the priesthood of all believers and our direct unmediated access to God through prayer. Martin Luther and the Protestant church reacted to this by encouraging the most literal interpretation possible, which in the case of Genesis gave us young-earth creationism.
In Biblical interpretation (exegesis), it's important to take an originalist view rather than a textualist one. The contains many styles of literature, not all of which are suitable for literal interpretation. When Jesus says "I am the true vine," he doesn't mean he has leaves, and when he says "I am the door," he doesn't mean he has hinges. If you are looking for the meaning, it is immediately apparent; if you strive for a literal meaning, it is absurd.
Or take this beautiful passage from Job:
Then the LORD answered Job out of the storm. He said:
"Who is this that darkens my counsel
with words without knowledge?
Brace yourself like a man;
I will question you,
and you shall answer me.
"Where were you when I laid the earth's foundation?
Tell me, if you understand.
Who marked off its dimensions? Surely you know!
Who stretched a measuring line across it?
On what were its footings set,
or who laid its cornerstone-
while the morning stars sang together
and all the angels shouted for joy? (Job 38:1-7, NIV)
The Bible only needs one true meaning. Even if you thought the Earth was flat, you would not imagine that instructing the reader about geology was point of this passage. You don't need to know that the Earth is round to see that this is about God's incomparable majesty, not the Earth's construction. And that's why early Christians were generally not confused by Genesis.
It is impossible to look at Genesis and believe that its main intent is natural history. It makes a spectacularly bad natural history. Light is created on the first day, and there is evening and morning each day, but the Sun, Moon, and stars aren't created until the fourth day. What was evening and morning with no sun? Where was the light coming from? A natural history would answer this; Genesis does not because that's not the point. Or, Genesis says,
And God said, "Let the water teem with living creatures, and let birds fly above the earth across the expanse of the sky." So God created the great creatures of the sea and every living and moving thing with which the water teems, according to their kinds, and every winged bird according to its kind. And God saw that it was good. God blessed them and said, "Be fruitful and increase in number and fill the water in the seas, and let the birds increase on the earth." And there was evening, and there was morning &mdash the fifth day.So when were grasshoppers or cockroaches created? They move along the ground sometimes, and fly sometimes. Or bees, or bats? How about all the sessile sea animals? They aren't plants but they don't move. Natural history was never the intention.
And God said, "Let the land produce living creatures according to their kinds: livestock, creatures that move along the ground, and wild animals, each according to its kind." And it was so. God made the wild animals according to their kinds, the livestock according to their kinds, and all the creatures that move along the ground according to their kinds. And God saw that it was good. (Genesis 1:20-25)
I can't imagine anyone who's been a serious churchgoer and didn't hear a sermon on Genesis. There must be tens of thousands of volumes of commentary that have been written about it. But all of these words fail to convey more about human nature and God's nature than the compact little story as it is. It doesn't need to be natural history to be true.
I have some more words for young-earth creationists:
Therefore each of you must put off falsehood and speak truthfully to his neighbor, for we are all members of one body. (Ephesians 4:25, NIV)Young-earthers tend to display a horrifying indifference to the truth of what they say. Almost all the science is nonsense, only fit to deceive people who know nothing of the field; much of it is based on never having bothered to really understand Darwin in the first place. When you point out that one scientific claim is false, they just move on to another from the same bogus-science source. A bunch of little lies cannot shore up a big truth. When a Christian find out that one of the claims they've been repeating is a lie, that is "disgraceful and dangerous" as Augustine puts it, and they've been making Christians look vastly ignorant, they should step back from all the ideas they got from that source. Learn about each topic before you repeat it; learn the reasoning of the enormous majority of scientists who think that the young-earth claim is wrong. This page, http://www.godandscience.org/apologetics/creation.html is a really good start but it's down as I write this.
Or if that's too hard, (and deeply understanding some things like radiometric dating is hard), don't say anything about it. Learn from Paul:
For I resolved to know nothing while I was with you except Jesus Christ and him crucified. (1 Corinthians 2:2)