It's a very excellent book, I'm amazed at the amount of research, evidence, etc he has in there. And he's very carful not to claim, "it's proven!"
I'm only 1/2 way thru the book. It's all about the melting at the end of the last ice age.
Right now I'm reading about India -- specifically, "Kumari Kandam", an 'atlantis' type lost civilization that was suppose to be south of India. And Hancock got maps of what the sea levels were 12000 to 9000 years ago, and sure enough, Sri Lanka was once connected, and they've already found ruins under the sea.
I'm a big fan of this kind of stuff, and I'm amazed I've never heard of it before.
From the sketchy research I've done on the Rig Veda, internal clues point to it being written in the Bronze Age (NLT 1200 BCE) in India. Other clues make the earliest it could possibly have been written about 1500 BCE.