The words, ‘this was the scroll’ imply that the previous words in Genesis 1 came from a pre-recorded source.
Also, the cadence of the words indicate that it was originally a poem or a song.
When was this portion of the Genesis written?
Unlike later portions of Genesis, the language used here indicates that it was likely transcribed by Moses into his (what was then) more modern dialect of Hebrew from a far older document.
For more information, see the commentary, The Bible’s Internal Proofs of its Authenticity.
Our Bible uses older manuscripts than most Bibles do. Check us out!