Evolutionary theory is a something of a science only as long it is a theorectical one. Not a pure science such as determining the weight of oxygen as many examples.
That's completely wrong, and it shows a lack of understanding regarding what science is about.
Science can never be 100% sure something is right. It is about finding the best model to fit the facts. The models are basically always imperfect to some degree (with important ones to a very, very small degree). Determining the mass of oxygen requires a reliance on these imperfect models, but they are still very good models to go by. Why? Because when we find out they have mistakes, we fix them to the best of our ability. So the error in them goes down over time. The Theories regarding Evolution is a model that fits all of the facts, and like Gravity, they probably have some errors, but the general principle is as sound as possible (short of some god-like entity faking the fossil record). Certainly there are no alternative theories that fit the facts well, so it seems evolution is by far the best explanation, even the only real general explanation, we have for determining how life changes over time.
Creationism, on the other hand, doesn't change to fit the facts, and isn't a science. It is dogma. It is worthless as a science and always shall be. Unlike evolution, the creationist model isn't changed or modified when new facts are uncovered.
Going over it again: A Scientific Theory tries to model reality in some way. Some scientists work on the theories, some work on uncovering more facts regarding reality. If we uncover evidence that a scientific theory isn't working somewhere, then scientists go back to the theory and change it or replace it (e.g. Newtonian Mechanics with Relativistic). That doesn't mean that old theory was bad necessarily, because it could be very good within a certain subset of the universe (e.g. Newtonian Mechanics and low-velocity, low-gravity areas). What it does mean is that the old theory wasn't complete, and there is no theory that will probably ever be complete. Very, very accurate in terms of explaining reality and predicting what we will find in the future when we look around (e.g. evolution), but there will probably always be some gaps. Now, some gaps doesn't mean the theory is bad, as I have said, merely that it is incomplete. (However, creationism IS bad, and it can't be fixed to account for reality, unless you have god making the fossil record and genetics to fool us, which is NOT a valid scientific theory because it deals with something for which we have no evidence -- a meddlesome god-like entity).