Kelly I don't have all the answers you asked for, but I saw a Creationist series about a week ago.  Many people think that the earth before the flood of Noah was quite different from today.  It had a firmament  that was mentioned in Genesis.   One of the places the water came from was "above the firmament".  There is an hypothesis that this firmament protected the Earth from UV light, kept the air pressure about twice what it is today, and kept the water cycle in equilibrium (no storms, just water vapor like a terrarium).
 
The increased air pressure would have made it about 3 times easier to breath.  Living things could have grown much larger and lived longer.  They also would have been protected from mutations from UV light.
 
I will try to get you a website where you can read more.  I don't envy you teaching science in a public school.

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Searching the web, I found www.AnswersMagazine.com.  At the bottom of their home page, you can click on questions similar to the ones you were asking.  Also there is a New Answers Book that addresses Creation versus evolution topics.  I hope this helps.