Its not that Creationism is impossible. Its not that it doesn't make sense. Its the simple fact of how impropable it is for some being from the heavens (or cosmos--whichever way you'd like to look at it) to suddenly snap his/her/its fingers and the first humans appear on Earth.
This is how I generally think of the Bible, God, and all of that: Sometime early in the human race, someone had the brilliant idea of how to control people. You take an all-knowing being that can strike people dead, and that thinks you're right--and get some people to believe--boom: instant command.
I think the Bible and God arose as a form of power over everybody else. Think of how, in the middle ages over in Europe (and even now, to a certain degree) how much influence the church had. Why? Well, would you want to piss off someone who could call on God and strike you down dead?
The fact is, people are so threatened by going to Hell and want to go to Heaven (which, in effect, creates a system of basic morals and values that I thank God--haha--that we have) and of pissing off the big guy upstairs, that they WILL follow whatever the church has to say. The system is psychological.
Think of it: Your whole life, your parents talk about God. If they don't, you know at least 50 other people who do. You see on television, on the movies. There are buildings in his name. So, even if the idea is absolutly NUTS (because, when you really think about it--what are the odds?) you come to accept it. Eventually, you come to believe it, and try to pass it down to others.
The fact is, even if what I say it true, religion is an ESSENTIAL part of what goes in on our world. It gives us a set of rules to abide by. If there was no religion, complete anarchy would unfurl: chaos in the streets, murders, rapes, and that sort happening everywhere, because no one feels they need to follow the rules anymore. Society relies on religion to survive (and there is strong evidence that many an empire has crumbled from religion) and be run properly, as does religion serve its purpose by controlling society.
In short, evolution doesn't make much sense either: as you already stated, 99% of all creatures that have evolved, the preceeding race had dissapeared.
My theory on evolution--and believe me, I have many--is that we evolved to adapt to a changing planet. Maybe it was an ice age. Maybe it was a global warming. The fact is, something probably forced some animal to evolve, and that power that did it was so gradual that it allowed the animal (whose to say it was apes? For all we know, it could've been fish!) to adapt to it. Apparently, this meant an intellegent retune--quite literally.
So, evolution seems more plausile, per se'; but that isn't to say that the idea of a far-fetched theory such as creationism isn't true.
For all we know, an alien race that resides millions of light years from our planet fired an alien spore which spawned all life on our planet. We could simply be some accident of Earth chemistry. We could all be intangible masses living in some fish's mind!
These are questions that have arisen since the dawn of mankind. I see no closure on these questions anytime soon, and just as well--
Some things are better left a mystery.