I am pretty passionate about defending Genesis 1's account of Creation and the later descriptions of the flood of Noah as literal. I believe it there is no reason, scientific or otherwise, to doubt them—and I believe our stand on them is of tremendous importance. I believe that the Gospel (and our outlook on future judgment) hinges on the truth of Genesis 1 and the judgment of Noah's flood, and that there is no other true way to explain death as a wage of sin, or to trust either the Bible or Jesus' words (Who spoke of Creation and the flood as literal), without trusting in both as literal and true.
In my experience, the primary reason people start to doubt them or to try and compromise with them is because of an underlying assumption of vast periods of time being needed to create what we see around us and in space. Basically the two schools of belief divide along these lines—either slow change over long periods of time, or rapid change driven by major cataclysmic events (i.e. a global flood and the fountains of the deep opening up) over a short period of time. Our educational systems (including some Christian, of which I have friends in) have seemed to have bought, without question, that what we see is the result of vast periods of time and gradual change.
Unbiased science, however, does not support this—and yet we teach it and receive it as truth instead of just another belief system or theory. If you want evidence of massive geological change over short time look at a Creationist account of what happened at Mount St. Helens. It was that experience that turned my friend, Dr. Rick Oliver of Confound the Wise Ministries, from an avid anti-Christian with a PhD. in Evolutionary Biology into a Genesis defending scientist. What happened there in a very short time turned upside down the teaching of how much time is required for major geological change—and Mt. St. Helens was not a large volcano in terms of what is believed existed some time ago.
Look also at the errors in scientific dating methods and, even more importantly, the underlying assumptions that are made in the dating methods. Whether mechanical (carbon dating, etc.), or by association (strata dating, etc.), there are tremendous assumptions made that are embedded in a prior belief of vast periods of time. Then, with that prior belief, we develop dating that substantiates it. Then all these "educated" men and women come out touting eons of ages and we, as Christians, intimidated, try and come up with theories to mesh "science" and the Bible.
Simply look at the advances of man within the last 150 years and I think you'll see that man doesn't require a lot of time to advance rapidly. In 1903 the Wright Brothers took the first 12 seconds of powered flight. By the middle to end of the next decade planes were flying bombing runs and dogfighting in the sky, and within 66 years of their flight we were sending men to the moon and bringing them back. Many of you readers will remember the first home computers and the massive, room-filling more "advanced" computers of just a few decades ago . . . and now most people in America have, as a "necessity," phones and tablets that are tiny and yet vastly more powerful and all connected around the world with wireless technology. We fought the war of 1812 (and wars much later, including our Civil War) with sailing ships. Today, only 200 years after the war of 1812, and only 150 years after the Civil War, we have nuclear powered super carriers that can go over 25 years (yes, years!) without refueling, and are over three football fields long (the Enterprise is, according to Wikipedia, 1,123 feet long—almost four football fields!). Only one hundred and fifty years ago this coming November Richard Gatling patented his Gatling gun which would revolutionize warfare . . . and in only a little over 80 years after that, in 1945, war would be turned upside down forever by atomic bombs that would do to entire regions and cities what the Gatling gun did to an advancing small body of men.
We could go on and on in all fields—medicine, technology, science, etc.—but it is clear, man doesn't require long periods of time to rapidly advance, and nor does geology . . . especially when you add to Creation the realization that God probably created with an appearance of age, and that there was a massive global upheaval and flood from both within and above after that. We must, I believe, if we and our generations are going to remain and stand confident in the Bible and God, question why we ever doubt it and realize that we are buying into assumptions and theories that are laden with guesses, falsehoods, and bias. Let every man be a liar, God is still true, and He always will be.