> The windows on tall buildings don't open, which is not a coincidence. Humans can't survive for very long 50+ stories in the air either. 50+ stories is signif

> The windows on tall buildings don't open, which is not a coincidence. Humans can't survive for very long 50+ stories in the air either. 50+ stories is significantly less than the difference between my altitude and the altitude of many perfectly happy civilisations. The reason windows don't open is that there are significant issues with cooling and regulating air pressure in a building that large. It has little to do with anything like oxygen concentration or even temperature.