In other words, we can't know everything right away. This wouldn't be science.
It seems strange to me that some people demand that science brings all the answers. Actually it's the difference between, for instance, a holy scripture and science. One is supposed to contain everything needed, while the other is continuously unfolding mysteries. No science manual is holy.
Sometimes I wonder if lack of self-confidence is not the main reason why creationists won't open their minds. We have to trust our own intelligence, without overestimating it.