Re: Would a flood covering the entire earth (as with 'Noah's Ark') be possible?

Dear Andrew:  The short answer is:  no.

There is not enough water to cover the entire earth unless the Earth's 
surface was essentially flat (devoid of mountains and large depressions 
like the ocean basins). The Earth's surface has never been flat, at least 
not in the past few billion years. 

One could of course add water to the Earth, but the only practical methods 
would involve moving comets (which are mostly ice) to the Earth. The 
impacts of enough cometary material on the Earth's surface to flood that 
surface would wipe out all higher life forms on the planet, making the 
question of what the flood itself would be like of interest only to 
extraterrestrials. 

There is really no answer to the salt-water vs. freshwater question because 
no such flood is possible except as outlined above.

The size of ark need to carry all flightless land-dwelling animals could in 
principle be calculated. However, many species of birds could not survive 
for long without a place to land or require food only found on land, and so 
they would have to be included as well. I don't have at my fingertips the 
necessary information, but this is what you would need to know:

1. sizes and weights of all animals to be put on the ark

2. minimum breeding populations (not always two; some parthenogenetic 
lizards would need only one individual; some gregarious species might need 
more than two)

3. total mass of food and fresh water required

4. area required for animals that need to move around to be healthy

5. Many species require special habitats and special foods. All of these 
would have to be provided.

I think a few minutes of rough calculations would show that such an "ark" 
would have to be many times larger than the largest vessel in existence, 
and probably larger than our technology and economic resources would 
permit. In other words, there's no practical way to house the more than 
1,000,000 terrestrial species of animals, and everything they'd need to 
survive, in any vessel we can build on Earth. In addition, many kinds 
of plants cannot survive inundation by water, and so you really would 
need propagules of these on the ark as well.

Now, if you want to build a space habitat for them, size is less of a 
problem, but it will be expensive to loft everything that you need into 
orbit.  

Hope this helps,
David Kopaska-Merkel
Geological Survey of Alabama
PO Box O
Tuscaloosa AL 35486