Where Did the Water Come From?
The first consideration is how much water it would take to flood the earth. The Society's publications consistently say that before the Flood, mountains were much lower than they are now. How much lower is never discussed, but Genesis clearly says the earth had mountains for the Flood to cover.
For purposes of illustration, let's pick a very low height for the highest mountains before the Flood and examine the consequences. Let's say the highest mountains were 114 feet above sea level. The Bible says the waters overwhelmed the mountaintops by 15 cubits, or 22 feet. Add that to the 114 foot mountain height and you get 136 feet. Now, the weight of water is such that a column of water 34 feet high weighs the same as a similar column of air extended to the limits of the atmosphere. A column one square inch in cross section weighs 14.7 lbs. This size column is used to define the standard atmospheric pressure of 14.7 lbs. per square inch. Looked at another way, this means that the pressure increase from the top of the atmosphere to the bottom is the same as the pressure increase from the top of 34 feet of water to the bottom. A consequence of this is that at sea level a pump can pull water only to a height of about 34 feet. In general, pressure can be measured in terms of equivalent atmospheres: one atm. of pressure is defined as 14.7 lbs. per square inch, because that is the pressure of the atmosphere at sea level. Similarly, the pressure 34 feet down in the ocean is 2 atm. (1 atm. for the water and 1 atm. for the air). Therefore the pressure at the bottom of a 136 foot deep body of water is 5 atm. (136 / 34 = 4 atm. for the water, plus 1 atm. for the air). Here is the point -- if that 136 foot depth of water covered the earth, and was then lifted up so that it became suspended in the atmosphere, the pressure at what was the bottom would still be 5 atm. This is simply because the atmosphere would be holding up the water, and the laws of physics say that for a fluid acted upon by a gravity field, the pressure at the bottom of the fluid is proportional to the weight of all the fluid above, whether that fluid be water, water vapor or air.
Apply the foregoing to the "waters suspended above the expanse." If the waters were held up by the atmosphere, they would be part of the atmosphere, and the pressure at the surface of the earth would have to be equal to 1 atm. plus the pressure due to the weight of the suspended waters. This has consequences for animal and plant life, as they can only take so much pressure before their biological processes are disrupted. Therefore, you may say, maybe the waters were held up by means other than being suspended in the atmosphere. Well, what are the means in general for suspending a thing above the earth? There are only two non-miraculous possibilities: either it has mechanical support, or the thing has to be in orbit. If you disagree, then what are the other possibilities? As for miraculous means of support of the water, it is not reasonable to suppose that God would suspend physical law for the billions of years from the beginning of creation to the Flood, or for the hundreds of millions of years of the history of life, or even from the start of the second creative day. Nor would he permanently change physical law just for the sake of causing the Flood. And it is not possible that the water canopy was in orbit like a satellite. Physical law says that if distributed material is in orbit it must assume the shape of a flat ring, like the rings of Saturn. An orbiting shell or canopy is not physically possible because only a relatively tiny portion of it could have the proper orbital velocity. The rest would fall down or fly off into space. So the only reasonable possibility to suspend the water is the mechanical means of atmospheric pressure.
Now, as mentioned above, oxygen breathing animals can only take so much pressure. A creature would not be crushed by the pressure, but would be poisoned by too much oxygen, or its body chemistry would not function properly. This is shown by the precautions that deep-sea divers have to take when diving below about 150 feet, at a pressure of about 5 atm. They have to replace the nitrogen in the air with helium, an inert gas, and reduce the oxygen concentration. If nitrogen is not replaced or if the oxygen concentration is not reduced, the body chemistry is poisoned. Too much oxygen, for example, produces hyperventilation and delirium.
This places a severe limit on how much water could be suspended above the earth. Man requires special measures to live in an atmospheric pressure greater than 5 atm., so the Flood depth had to be limited to at most about a hundred feet, as seen from the above discussion. If the depth was not so severely limited, you would have to propose radical changes in physical law, or in the body chemistry of virtually all animals, so they could survive in the radically changed atmospheric conditions after the Flood. There is no evidence such a thing has occurred.
Another problem related to atmospheric pressure, which I've never seen discussed, is related to the design of flying creatures. Such creatures -- insects, pterosaurs, birds, bats -- have been around a long time, long before any Flood occurred. The design of a flying creature must account for air density. Birds are wonderful examples of optimal design, and their design shows they were made to fly in air that has the present density. They have powerful wing muscles and respiratory systems optimized for strenuous effort in the thin air of high altitudes. Had there been a thick vapor canopy before the Flood, held above the earth by physical processes operating today and not by miracles, the air would have been much denser than it is now. Birds would not have had to work nearly as hard to fly as they do now. If they had the same design as today, they would not have been optimally designed for conditions then. They would have needed much smaller wings and had different respiratory requirements, to name just two. This fact alone is compelling evidence that a thick vapor canopy never existed, but that atmospheric conditions have been similar to today's as long as flying creatures have existed.
If my proposed depth for the Flood of about a hundred feet seems unreasonably low, think what happens to atmospheric pressure as the proposed depth is increased. The pressure problem gets worse. But some creationists propose another source for the water. Genesis says that the source of the waters was not only the floodgates of the heavens but also the "vast springs of the watery deep." If we assume that the watery deep refers to the earth, such as subterranean caverns, and limit the amount of water above the "expanse" to 1 atm. worth, enough to provide 40 days of rain, and propose that the vast majority of the Flood water came from the springs of the watery deep, the pressure problem goes away. Then the depth of the Flood could potentially be thousands of feet, a much more reasonable value. But there are no subterranean caverns today that hold huge quantities of water, nor is there evidence that there ever were such. In fact such caverns could not exist:
Another possibility for obtaining the required water is from the earth's mantle. It has been estimated that in the mantle is dissolved about 3400 times as much water as is in the ocean.49 But extracting this water, of course, requires a miracle.
There are other difficulties related to the scenarios described above. Zoologist Michael Archer described the results if enough water to flood the earth deep enough to cover today's mountains suddenly became available:50
Note the problems all this excess heat causes for the claim that the Flood produced the frozen mammoths of Siberia. Someone might object that it would be easy for God to remove the excess heat. If he did all this, it seems a rather round-about way to destroy all the inhabitants of the earth. Why not create the water out of nothing, or even simpler, just destroy the source of the problem -- men?
The above arguments indicate there appear to be only miraculous ways to obtain enough water to flood the earth and not destroy all life in the process. This difficulty is an important problem, but there is one even more important. Let's now examine the questions of where the water went after the Flood, how the continents and ocean basins got to be as they are, and other issues related to the height of mountains and the depth of the Flood.
45 Insight on the Scriptures, Vol. 1, p. 609, Watchtower Bible and Tract Society of New York, Inc., Brooklyn, NY, 1988.
46 The Watchtower, p. 420, Watchtower Bible and Tract Society of New York, Inc., Brooklyn, NY, July 15, 1968.
46a These are often based on an explanation from The Genesis Flood by John C. Whitcomb and Henry M. Morris, pp. 240-241, Baker Book House, Grand Rapids, MI, 1961,which says ".... the region above about 80 miles is very hot, over 100Deg F and possibly rising to 3000Deg F, and is in fact called the thermosphere for this reason. High temperature, of course, is the chief requisite for retaining a large quantity of water vapor. Furthermore, it is known that water vapor is substantially lighter than air and most of the other gases making up the atmosphere. There is thus nothing physically impossible about the concept of a vast thermal blanket once existing in the upper atmosphere."
The problem is that the atmosphere above 80 miles is extremely tenuous -- so tenuous that satellites can orbit at 100 miles. If the entire region above 80 miles were nothing but water vapor, at today's pressure, it would amount to only a small fraction of an inch if condensed and spread evenly over the surface of the earth. Also, the temperature is high because the upper atmosphere absorbs high energy radiation from the sun -- the thermosphere protects the earth's surface from ultraviolet and other types of radiation. If there were a thick vapor blanket up there, only the tenuous topmost portion would be hot, while the rest of it would be at much lower temperature, because it would be shielded from the radiation by the topmost layer. So the idea that a vast thermal blanket once existed in the upper atmosphere and provided enough water to flood the earth is not physically reasonable.
47 Insight on the Scriptures, Vol. 1, p. 610, Watchtower Bible and Tract Society of New York, Inc., Brooklyn, NY, 1988.
48 Norman D. Newell, Creation and Evolution: Myth or Reality?, pp. 37-38, Columbia University Press, New York, 1982.
49 H. W. Menard, Islands, p. 77, Scientific American Books, Inc., New York, 1986.
50 D. R. Selkirk and F. J. Burrows, editors, Confronting Creationism: Defending Darwin, New South Wales University Press, Kensington NSW Australia, 1988.