How did Allah "peg" the mountains?

Mountains have deep roots within the Earth's crust and serve to stabilize the Earth. The Holy Quran mentioned this fact in His (Allah's) saying: {Have We not made the earth a resting place? And the mountains as stakes?} [Quran 78:6-7], and His saying: {And He has cast into the earth firmly set mountains, lest it should sway with you;} [Quran 16:15]. This fact was only discovered recently.