Why don't creationists teach a literal firmament anymore? People don't seem to believe in the firmament as a literal barrier of water up in the sky that collapsed at Noah's flood. I want to say they don't believe in the firmament anymore, but I am doubtful most creationists did. Why? Is it because it is too fantastical?

The problem is that such a notion seems to correlate with Genesis and seems to make a lot of other considerations more swallowable, such as the feasibility of centuries old lifespan, adequate conditions to sustain large animal life (dinosaurs, etc), and adequate water for a sudden flood. The only "scientific" model I've heard, coming from Dr Carl Baugh, asserts that waters from the deep under the earth came up and cracked open the firmament; his model is the only creation model that solves so many fundamental problems for creationism I am literally, truly perplexed as to how his model has been seemingly abandoned by the creationist community. I know of no direct arguments against this sort of firmament, except only alternative interpretations of its mention in Genesis. What am I missing?

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It is the "canopy theory", I believe, that I had in mind in posting the question. My own only exposure to this was from a presentation by Dr Carl Baugh and by reading his old book, Panorama of Creation. I have had difficulty finding anyone endorsing his model, and his model is the only one that answers several questions. My frustration comes out of watching modern depictions via illustrations, 3D graphics, and simulated film artwork, attempting to use fine detail to tell what Genesis earth was like but not filling in these gaps. Blue skies, clouds, rainbows, all post-Noah, all completely against Baugh's model. Does it matter? In an age when modern illustrations like Hollywood are referenced in dialogue with apologetics and truth seekers, yes, I believe so.
People don't seem to believe in the firmament as a literal barrier of
  water up in the sky that collapsed at Noah's flood. 


The answer to this is amazingly simple.

Many Young-Earth Creationists believe that there was a layer of water of some form (ice, water, other possibilities) in the upper atmosphere, or in space, surrounding the earth AND Young-Earth Creationists believe that there is a Firmament.  

However, almost none believe that the Firmament is a solid layer of water because YEC-ers have a hyper-literal understanding of the Genesis account.  And...

It's impossible to get the idea that the firmament is a solid layer of water from the Genesis account.

That's the answer.  Here's the explanation:

From Genesis 1 (KJV)


  6 And God said, Let there be a firmament in the midst of the waters,
  and let it divide the waters from the waters.
  
  7 And God made the firmament, and divided the waters which were under
  the firmament from the waters which were above the firmament: and it
  was so.
  
  8 And God called the firmament Heaven. And the evening and the morning
  were the second day.


Jumping down to verse 20:


  20 And God said, Let the waters bring forth abundantly the moving
  creature that hath life, and fowl that may fly above the earth in the
  open firmament of heaven.


The Firmament is the place between the waters - it divides the waters above from below.  It's not a solid layer of water, it's the space between the waters.  It's where the birds fly.  It'd be a bit hard for birds to fly in a solid layer.

So, again, the reason Young Earth Creationists don't teach that the firmament is a solid layer of water is that YEC-ers are very literal in the interpretation of Genesis (by definition) and there's absolutely no way to get the idea that the firmament is a solid layer of water from the text.

The idea, however, that the layer of water (in whatever form it took) was part of the source of water for the flood (along with the fountains of the deep) is pretty common among Young-Earth creationists, however, and is taught widely.  

Details on the nature of the waters vary. Some say clouds or water vapors.  Others think a layer of ice in the upper atmosphere or in space. There's not much agreement on what form it took, but it is widely believed to have existed in some form.