A fierce debate rages in today's America about the origin of life. It is an incredibly important debate that I don't believe can be won by arguing scientific theories (e.g. Intelligent Design, Darwinian Evolution.) The primary reason it can't be won on scientific evidence is that people have made their minds up on the topic already and can support their position with science. What I believe Christians should do is focus on the implications of an origin without God and realize that God is bigger than this debate.
1. Implications of life without God
What is inherently better about "life"? What incentive do I have to preserve my existence or the existence of those around me? Why is preserving of a group of molecules that have somehow become self-aware more important than not? A true atheist has no answer. Any attempt answer that and you leave the realm of the natural and enter the supernatural.
If we are unable to answer that question, then everything falls apart. There is no authority; no authority for government, no authority for decency, no authority for morality. Without God no one could tell me that walking into your house and killing your family is wrong, or that walking into a classroom and shooting 32 people is wrong, or that people starving in Africa is wrong.
If atheists realized what they were saying they'd live differently or stop being atheists.
2. Evolution is not bigger than God
Let us assume scientists were to somehow discover "the missing link" or reproduce the "primordial soup" that resulted life, what then for the believer? Does God cease to exist? Is the Creation story now irrelevant and wrong? The answer, of course, is absolutely not. Rob Bell in his book "Velvet Elvis" takes this idea and expands it using the virgin birth to do so. He spends a little more time fleshing out the argument using bricks and trampolines as a metaphor, but I'll leave it at that and perhaps get him some more book sales. The heart of the matter is that we want to introduce people to God and not to a set of rules and doctrines that one can adhere to without knowing why.
As always there is plenty more to be said, but this at least gets some of the ideas out there.