Science and God

It always stumps me when someone uses scientific explanations to disprove God's existence. If God is truly the Supreme Being and Creator of All, wouldn’t he be the originator of science, too? Why do people try to separate science from God? If there are practical and scientific explanations for, let’s say, the parting of the Red Sea, or the plagues of ancient Egypt, or the Great Flood, couldn’t he, since he created the world, have arranged things to happen in a manner that is both scientific and reasonable to understand? Who drew that invisible line between the natural order of things and God?