This manga is available online at
http://www.tokyopop.com/mangaonline (only one chapter a month, probably only for the first volume). I've read three chapters, including the first, and I believe I have a few things I need to say in this thread.
First, this story has next nothing to do with Noah. If not for the names and the word "ark" (which is hardly intellectual property of the Bible) it would have no connection whatsoever. The three girls go back in time to save species from extinction and put them in this Ark to prevent the gradual destruction of the Earth by mankind. That is all; it's barely based on Noah's Ark, much less a retelling of it.
Second, it isn't even operating under a biblical system. That is, it is an entirely different world with a very different cosmology. If the author twisted anything to get her manga, it was Angel Sanctuary, not Genesis. As far as religion goes it seems to operate based on a sort of pantheism: there is a spirit that both guards and
is Earth, as well as ones for other planets, other natural forces, as well as a life force overall.
Lastly, though I don't have a problem with the series, I've been very unimpressed with it. I wanted to read it because it was free and highly rated by users, but I couldn't make myself read more than a few chapters (and this is one chapter a month). I'm unfamiliar with the artist's background and I don't want to assume too much, but the plot and art strike me as so CLAMP-derivative that I'd call it a knock-off. Not something I'll be pursuing in any case.