My question for creationists is how can evolution not be possible?
First, there are different alleles out there in any population and it is reasonable to assume that some of them may lead to differential reproductive results, which would change the overall population of existing alleles.
In addition, we know that there are mutations going on all the time as well. For example, a study of 78 Icelandic families whose genealogies were well known sequenced the genomes of 219 distinct individuals (Kong, A., et al. (2012) Rate of de novo mutations and the importance of father's age to disease risk. Nature 488:471-475. [doi: 10.1038/nature11396]) and found there are about 77 mutations per generation.
So isn't it likely that over billions of generations that there will be significant genetic change based on the interaction between the environment and the reproductive success of individuals?
At the same time, I totally think that biogenesis itself is not understood at all by science - there are just wild guesses right now. I give creationists cover if they want to say that no one really knows how biogenesis happened, but once we get to cells and DNA, the rest is pretty easy to work out.