Therefore, water can either orbit the earth (something like the ice rings of Saturn)
Yep, that's what I was getting at. Evermore has posted the standard argument that if the canopy was high enough to be ice, it would have raised the temperature considerably when it fell. I'm honestly not sure anyone has actually proven that rigorously, but it seems believable given that we are talking about 40 continuous days of rainfall.
And the argument that, in any form, that much water would have obscured the sun, moon and stars seems pretty irrefutable. Even as ice the canopy would probably be so thick that it would block or distort the light.
As for the effect on carbon dating - I’m going to have to re-think that… my head hurts.
Okay, so I'm sorry for wasting your time with that, just forget you read it :-| I did some reading on C14 dating, and it turns out I didn't understand the process. I thought the breakdown of C14 came from atmospheric radiation, but that's what produces C14. C14 just naturally decays at the same rate no matter what, which I should have known.
So actually I guess creationists can suggest that, since the canopy lowered the radiation reaching our atmosphere, that would mean less C14 was produced. So that would mean that a pre-Flood sample would contain a lower ratio of C14 to C12 at a given age than scientists would expect. In other words, they would overestimate the age of the sample because they would think it must have been around a lot longer to have decayed down to that ratio.
This is what I get for not reading about dating methods since I stopped being a believing Witness. I guess I still have a lot of self-education to do.