science just is. we have created the means necessary to understand it. the language we have created, the means we have defined, the applications we have designed... those are the accomplishments. the science would be ongoing without us.
Well, imho the most important creation - invention, whatever, has to be farming. Man lived for hundreds of thousands of years as hunter-gatherers in what is known as the Paleolithic. Once we figured out how to plant crops, keep the best seeds to do so again later, it changed everything.
science is too broad. Science is an aspect everything. I guess i see the philosophical question you're posing, but science is not a creation, it is a method. I would describe science as invaluable. It is the way that we naturally think. It just "clicks". It makes sense to draw conclusions based on empirical observations, and we do it all the time without even thinking about it. This, along with more technical science has gone on for as long as man has existed with this degree of intelligence and awareness. Perhaps it wasnt known as science and was less concrete, but it certainly was science. Science is similar to experience.