The seven day week was ordained in the Torah, looooooooooong
before the Captivity. Prove it. Sure, the seven-day week appears
in Genesis, but this didn't achieve its present form until 500
BCE or so, or about a century after the Captivity. It could well
be a late addition. I cannot, with my current resources/fund of
knowledge, prove that the seven-day week appears in a pre-
Captivity manuscript of the Torah. However, you, in order to be
fair, must hold yourself to the same standard you're holding me
to. Therefore, the onus of proof is still on you. Because I hold
the position that (though I personally cannot prove) has been
widely accepted and has no evidence to contradict it as far as I
know. So, you must show me that Babylon had the seven-day week
before any contact with the Jews for your hypothesis to be
correct. The only calendar change I'm aware of that resulted
from the Babylonian Captivity is the renaming of the months.
Possibly the Babylonians came up with it concurrently, or the
Jews gave it to them?