As altitude increases atmospheric pressure and oxygen concentration in the atmosphere decreases. A point is reached where humans cannot breath anymore.
Effects of high altitude on humansDeath zoneThe death zone, in mountaineering, refers to altitudes above a certain point where the amount of oxygen is insufficient to sustain human life for an extended time span. This point is generally tagged as 8,000 m (26,000 ft, less than 356 millibars of atmospheric pressure).
Humans cannot breath at high altitude. Above the death zone you have to bring your own oxygen. This was only known recently, however this was portrayed in the Quran 1400 years before it was discovered. The Quran says that as we ascend to the sky it becomes more difficult for us to breathe:
١٢٥ فَمَنْ يُرِدِ اللَّهُ أَنْ يَهْدِيَهُ يَشْرَحْ صَدْرَهُ لِلْإِسْلَامِ ۖ وَمَنْ يُرِدْ أَنْ يُضِلَّهُ يَجْعَلْ صَدْرَهُ ضَيِّقًا حَرَجًا كَأَنَّمَا يَصَّعَّدُ فِي السَّمَاءِ ۚ كَذَٰلِكَ يَجْعَلُ اللَّهُ الرِّجْسَ عَلَى الَّذِينَ لَا يُؤْمِنُونَ
"He makes their chests tight and constricted, as if they are ascending to the sky" this turned-out to be correct. No mistakes in the Quran.
How could an illiterate man who lived 1400 years ago have known how altitude affects breathing?
The Quran (Koran, the book of Islam) contains scientific knowledge that could not have been known 1400 years ago. It ranges from basic arithmetics to the most advanced topics in astrophysics. You are invited to go through those miracles and judge for yourself.