How do we know what with Adam and Eve in the Garden of Eden?

There are two different ideas of how Moses received the information about what happened throughout the entire book of Genesis.  The first view states that it was handed down orally from Adam to others.  This would be plausible, considering that it would go from Adam to Methuselah to Noah to Terah to Abraham to Jacob to Joseph and a couple more generations to Moses; not very many people at all.  The other view is that God simply revealed all these things to Moses.  This view would make more sense as there are things recorded that other people may not know about.  Also, the first view tries to give a more humanistic view of how it could have happened and take God out of it.  A third option is that it could have been a combination of both.  Either way, it is easily explained how Moses received this information.