How did we get the first chapter of the Book of Genesis?

How did we know about the finest details of creation, if no one was there to witness it. The first chapter in Genesis and part of the second chapter (verses 1:1-2:4a, the first sentence in 2:4) form a completely different creation story from that in Genesis 2:4b-20. At first, the Book of Genesis did commence with the second sentence in verse 2:4, but an anonymous source now known as the priestly source added verses 1:1-2:4a during the Babylonian Exile. The Priestly source was inspired by a creation story found in Babylon during the Exile.

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