Does theistic evolution undermine the authority of scripture? First of all, why do I even ask the question? It came up during a conversation on Facebook. Where all good questions come from!
The answer to the question is NO.
Why doesn't theistic evolution (or evolutionary creationism) undermine the authority of scripture? Because the Bible is not a science book. Genesis one was never intended to tell us about how the universe was created.
The Bible is a reliable source of information about God and his plan for humanity. The first chapter of Genesis is a creation hymn of the ancient Israelites that was intended to differentiate them from the rest of the Ancient Near Eastern World. It was to show that one God created the world instead of the pantheon of gods that other civilizations claimed.
Even though I firmly believe in evolutionary creationism, I take the Bible very seriously. The Bible was inspired by God. It is not to be taken lightly. But, neither is it to be always read literally. Every portion of the Bible was written in a certain time and place and to a certain people. It is our responsibility as readers of the Bible to learn all we can about the context of the text so that we can make a reasonable interpretation.
So, when we read the first chapter in Genesis, we see that it is a poetic hymn written by a pre-scientific people. (Note: Calling ancient Israelites "pre-scientific" is not intended to be disparaging. These people were intelligent, but their culture had not yet developed the scientific method so their understanding of the universe was different from ours.) Reading the Bible this way is not frivolous or "loose". It is trying to understand the text for what it is.
For more reading on this topic, I would highly recommend anything on the BioLogs website or anything by Denis Lamoreux, a theologian and biologist.