I want to know the arguments before I start arguing.
Lots of creos have come here saying that. Very few of them have ever shown any real interest in trying to learn. However, I am willing to take you at your word for the moment, and will attempt to explain a few things to you.
Science is the process of making observations of the natural world, developing hypotheses to explain what we see, making predictions based on those hypotheses and testing those predictions by comparing them to further observations. That is how science works, in a nutshell.
You claim that we cannot know anything about the prehistoric past because nobody was there to observe it. Implicit in this claim is the idea that we can't know anything without direct observation. This idea is false, at least as far as science is concerned. Processes that occurred in the past left evidence behind. That evidence can be observed and hypotheses formed on the basis of those observations. Predictions can be made based on those hypotheses, and those predictions can be tested by further observations.
You may agree or disagree with the validity of this process as it applies to prehistoric events, but science relies on it every day, and it allows science make predictions about future discoveries that are borne out.
Those who would sacrifice an essential liberty for a temporary security will lose both, and deserve neither. -- Benjamin Franklin
We see monsters where science shows us windmills. -- Phat