IM: "--the same amount of gas is now spread over a greater circumference. But the difference would not be so great as to make breathing very difficult or impossible.
The Earth's circumference is 40 000 km The highest mountain ~ 10 km. so you are creating a higher circumference, 628 km longer. that is stretching the same gas into an 1.5 % greater volume. That is a fall of barometric pressure you would experience when rain is coming, so Noah, if there ever was one, could breath easy (except for the animal stench that wafted), as he drifted over Mount Everest. So: Sir Edmund Hillary was not the first man above Mt Everest, it was Noah, at altitude. now that's hilarious.