The book of Genesis was not written by eyewitnesses ... Moses wrote Genesis ... and he was not there ...
now ... perhaphs Moses had eyewitness SOURCES ...
THAT is a different issue ...
I beg to differ. The most recent, conservative scholarship shows that there is extremely strong evidence that Moses edited the clay tablets created by "eye-witness" authors. This is NOT JEPD...this is partially based on the scholarship of P.J. Wiseman. And this in no way impinges on the plenary inspiration of the Scriptures. I would be happy to point you to the research, but right now I am at the office and I don't have the information in front of me.
By the way, this is the part of the doctoral dissertation on Genesis that I am currently working on. It is, admittedly, not a widely held position, but the evidence is very strong, and very exciting. It shifts the authenticity question to much earlier to the actual events recorded in it.