There are lots of strange contradictions in the Bible. Cain was marked so that nobody who found him would attack him. But he and Abel were the only two children of Adam and Eve, so where did all these other people that might have found him come from? And yes, as you mentioned, there is the strange thing with Adam's first wife. And yet people say that every word of the Bible is literally true. I don't see how anybody who has read it carefully can possibly say that.