I don't know...is that ok?

I remember with fondness the sweet innocence of the year when my oldest daughter was 2. She was always curious, but at that age when she asked "why?" and "what is that?" I was able to answer these questions and move on with life in a somewhat satisfactory way. Pre-kid, I always thought it would be fun to have someone to share your knowledge with and answer those whys. If in a serious mood I could take on the scientific explanation of why the clouds look that way or if in a whimsical mood I could tell her they were big puffy marshmellows.
Now she is 4 and for the last 6 months I have been unable to answer a single why without a series of other whys that has left me wanting to smack my head against the wall. Her..."Why do workers cut down trees?" Me..."To make wood to build houses?" Her.."How do trees make wood?" Me..."It gets cut into logs and then cut into wood to make houses" Her..."What are logs?" It goes on and on... And not to supress her curiousity I try my best to answer her questions, but there is always a point where she backs me into a corner and I have to go into either "Because God made it that way" or quite simply "I don't know". Pulling the God card feels like cheating, but it is ironclad and difficult for even her to argue. I'm concerned about "I don't know". At 4, I feel that I should be much smarter than she is and knowledgable about most all things, but then there is the reality that I really don't know. And there is a part of me that wonders...is that ok?
As parents is that ok that we don't have all the answers? Will she think less of me? I don't remember my parents responses when asked a lot of questions, but I'm sure something like "that's enough" came into play if the questioning was going on too long. We have such a short time to be the ones they come to and ask questions. Soon they will be the experts on everything and nothing and we will have to wait until they are older and realize we might have a bit of information to share that could help them in their life's journey.
I hope the "I don't knows" won't make her think less of her mom, but rather make her realize that sometimes it is ok to not know the answer and have to ask others for help. And that is a lesson that will help her more in life than always knowing the whys.