For better or for worse, the word "theory" can entail either certitude or lack thereof. The former is typically understood by the scientific community, while the latter by common usage. Since evolutionism relies largely upon unobserved, unrecorded history, I tend to place it under the latter meaning. But then again, there may be someone around here who observed the formation of the world 4.5 billion years ago (and counting). You never know.
"Since evolutionism relies largely upon unobserved, unrecorded history, I tend to place it under the latter meaning."
Then your understanding of the evidence for evolution is sadly lacking. You may wish to review the evidence, starting with Darwin's observations, before rejecting them out of hand.
The scientific community has approached the theory with great skepticism. The fact that it is a "theory" at all shows how strong the evidence is for it - it's the only theory that fits.