Tectonics
Earth's crust has been slowly moving for billions of years. Not only mountains are still slowly moving but also whole continents. Moslems say that this is what Allah says:
[Quran 27.88] You see the mountains and think they are firmly fixed: but they are moving away just like the clouds are moving away: (such is) the artistry of Allah, Who disposes of all things in perfect order: for He knows all what you do.
How could an illiterate man who lived 1400 years ago have known that mountains move?