Did Noah need oxygen above the mountains?
Question: If mountain climbers need oxygen tanks to climb Mount Everest, how were Noah, his family, and the animals able to breathe on the Ark when they were above the mountains (‘ ... and the mountains were covered.’, Genesis 7:20)?
Answer: This question presupposes that Mount Everest was the height it is now (8,848 m = 29,028 ft), and that the air pressure would not have changed at that height above normal sea level with the addition of the flood water.
Mount Everest was not the height it is now during the Flood. Earth’s highest mountains have fossils of sea creatures at their tops, showing they were once under the sea. The possibilities are that the sea rose to cover the mountains, or the mountains were once under the sea and have since risen out of the sea, or a combination of the two.
Many creationist scientists think that mountains such as the Himalayas were probably built by catastrophic movement of the earth’s continental plates during and after the Flood (see Q&A: Plate Tectonics). Measurements indicate that the Himalayas are still rising. The rate of rise now measured is just the remnant of the processes that occurred much faster in the past.
Mountain building occurred as a part of the geologic processes that deepened the oceans to take the waters off the land towards the end of the Flood. Some mountains could have existed before the Flood, but none like the current Himalayas, Alps, or Andes in height. In any case, there is only enough water on all the earth to cover mountains about 3 km (2 miles) high, if all the ocean basins were raised. So, if the waters were not 9 km deep, but much less, the question is no longer an issue.
Even if the flood waters were 9 km deep, would Noah and company have had trouble breathing?
Absolutely not. Air pressure is caused by the weight of air above the point where the pressure is being experienced. If the water was 9 kilometres deep, then the air that was in that 9 kilometres deep volume of what was atmosphere would have been pushed out and would then have sat above the water at 9 kilometers above the earth’s former surface.
However, if we assume the worst case scenario of the radius of the earth increasing by 9 km due to the water, the surface area of the earth plus water would have been greater than the earth so that the weight of air would have been spread over a bigger area so that the pressure would have been less.
How much would the air pressure have been reduced? Less than 0.3%. This is equivalent to standing on top of a 30-m (100-ft) high building at sea level! There would also have been a negligible effect on the pressure due to changes in the force of gravity (which affects the weight of the air).
It is certain, therefore, that those on the Ark would have had no trouble breathing—without oxygen tanks.
Was the surface and water area of the earth different at the time of the flood. Ezra states this in his creation account in 2 Ezra 6. He states that at the time of creation the earth was 85% land, 15 % water. So a great amount of water was added to the earth at the time of the flood if the whole earth was to be covered by 2 km of water. I know this is not considered scriptural because Ezra's second book was removed from scripture as part of the Apocrypha in1545. Why is Ezra's account of creation never taken into account in your creation or the flood?
We don't know the relative amounts of land and sea pre-Flood.
The apocryphal books are not part of our Bibles for good reasons, and so we don't regard them as reliable sources. The book of 2 (or 4) Ezra/Esdras was probably compiled late in the first century AD (after the temple destruction).
If all the land were flattened the whole surface of the earth would be covered with about 2 miles of water. When the flood receded did the water find a hole to drain into or was the land pushed up to form the continents? I believe the latter. The rocks had to be bent and folded when they were soft. I don't care how slowly you bend a solid rock it is going to shatter long before it reaches 90+ degrees.
I fear you may have given the poser of this question too much credence as a scientific thinker, thus needing to overthink the answer. The answer is, in fact, much simpler.
Mountain climbers need oxygen on high mountains, not because they are so high from the sea floor or because they are so far from the centre of the earth, or anything like that. They need oxygen because they are so high above SEA LEVEL. Noah remained at sea level throughout the duration of the flood, until he exited the ark.
As the calculations show, there would be a tiny decrease in the partial pressure of oxygen due to the slightly greater circumference of the earth + water (sea level being higher).