Scientists DO know that evolution is a solid fact. They have mountains of evidence, indisputable fossils and whatnot.
- Tons of fossils distributed over large geological areas, all of which are compatible with the ideas of where animal X evolved into animal Z and unto Y.
- Humans and chimpanzees have 98% similar DNA
- Close morphological details between humans and apes
- Similar psychological and instinctive behaviours between humans and apes
- Macro-Evolution and Natural Selection can be observed in drug-resistant bacteria. (This doesn't really prove that humans evolved from an ape-like ancestor, but it does prove that evolution exists)
- Apes have *exactly* 1 chromosome more than humans (proves we're closely related)
Think of it as a giant puzzle where 75% of it is solved, and you can clearly see that it resembles a house. The remaining 25% of the pieces are missing, but does that really mean you can't conclude that it's a house? It's the most logical, reasonable explanation and you'd have to be pretty ding-dong (oh yes I did!) ignorant on the subject to refute it simply because the remaining pieces have yet to be found. It really doesn't get much simpler than that.
Whether we were created by some big bully who lives in the skies or not is irrelevant, because we know that evolution is for real, even if the theory has not been fully proved due to biologists not having obtained a complete, transitional fossil record. And even that is too much to ask for, because how do you expect them to find a well-observed fossil from every single generation within the last 3 billion years? (approximately how long evolution itself has occured on our planet)
Edit: there's also already a thread exactly like this.