Who wrote the book of Genesis and how was the information contained therein obtained?

After reading all the historical background of Genesis, I was thinking who wrote this? It seemed like such a simple question with a simple answer. The Book of Genesis starts with the creation of the Universe, Earth, water, air, animal, and finally man. But there is no mention on whom or how this Book can about. I was think of Noah. It just seemed to me that he would have enough on his plate with saving mankind that he would not be gathering up written documents.

 I started my search with http://en.wikipedia.org/wiki/Book_of_Genesis, and found that most people believe Moses wrote the Book of Genesis. Most scholars agree that the Pentateuch—which is the first five books of the Bible—was a collection of four sources. These sources are:  the Yahwist, the Elohist, the Deuteronomist and the Priestly source. Since the 1970s, the Elohist is now regarded as a variation of the Yahwist.

It was very interesting to see that on this site that they believe that the Yahwist was written in the court of Solomon.  They also know the author of the Priestly source to be Ezra in the 5^th century.  Now later thinking is that the Yahwist was written around the Babylonian Exile of the 6^th century. So this theory contradicts the idea of Moses writing the Pentateuch. He would not of been alive during Solomon's rein. So it would of been very hard for him to knock off these books.

They also attempt to explain a “why” to the Book of Genesis. Their explanation is: a theory which has gained considerable interest, although still controversial is "Persian imperial authorization". This proposes that the Persians, after their conquest of Babylon in 538 BC, agreed to grant Jerusalem a large measure of local autonomy within the empire, but required the local authorities to produce a single law code accepted by the entire community. The two powerful groups making up the community—the priestly families who controlled the Temple and who traced their foundation-myth to Moses and the wilderness wanderings, and the major landowning families who made up the "elders" and who traced their own origins to Abraham, who had "given" them the land—were in conflict over many issues, and each had its own "history of origins", but the Persian promise of greatly increased local autonomy for all provided a powerful incentive to cooperate in producing a single text.^[15]

It makes sense that the theory of the “Persian imperial authorization” would be over land disputes. Land disputes are still a major factor in this part of the world. It has been that way for ages which is depicted in the Bible beginning in the Book of Genesis.  Abraham and Lot left their families land to seek out a place of their own. Jacob and his sons were constantly moving around and claiming land. Land is livelihood to these nomadic people. It is what sets them apart from the rest.