As altitude increases the oxygen concentration and atmospheric pressure decreases. A point is reached where humans cannot breath anymore. The Quran says that as we ascend to the sky it becomes more difficult for us to breathe:
[Quran 6.125] Those whom Allah wants to guide, He opens their chests to Islam; And those whom He wants to leave astray, He makes their chests tight and constricted, as if they are ascending to the sky: Such is the penalty of Allah on those who refuse to believe.
How could an illiterate man who lived 1400 years ago have known that we cannot breath with increased altitude?
The atmosphere protects Earth from harmful cosmic radiations. It also protects Earth from meteorites and small debris bombardment.
[Quran 21.32] And We made the sky a protective shield and they turn away from its sign.
How could an illiterate man who lived 1400 years ago have known the protective function of the atmosphere?
1400 years ago the highest altitude a man could fly was the height that he could jump. But the Quran foretold them that man someday will reach the sky.
[Quran 29.22] You cannot escape (Allah's might), on earth or in the sky; and you have no protector and no savior besides Allah.
How could an illiterate man who lived 1400 years ago have known that man will reach the sky?