The Quran

أَفَلَم يَرَوا إِلىٰ ما بَينَ أَيديهِم وَما خَلفَهُم مِنَ السَّماءِ وَالأَرضِ ۚ إِن نَشَأ نَخسِف بِهِمُ الأَرضَ أَو نُسقِط عَلَيهِم كِسَفًا مِنَ السَّماءِ ۚ إِنَّ في ذٰلِكَ لَآيَةً لِكُلِّ عَبدٍ مُنيبٍ

Muhammad Asad

Are they, then, not aware of how little of the sky and the earth lies open before them, and how much is hidden from them?¹ - [or that,] if We so willed, We could cause the earth to swallow them,² orcause fragments of the sky to fall down upon them?³ In all this, behold, there is a message indeed forevery servant [of God] who is wont to turn unto Him [in repentance].⁴

Lit., "... not aware of what of the sky and the earth is between their hands, and what is behind them": an idiomatic phrase explained in surah 2, note 247. In the present context - as well as in 2:255 - the above phrase stresses the insignificance of the knowledge attained to by man, or accessible to him; hence, so the argument goes, how can anyone be so presumptuous as to deny the reality of resurrection and life after death, seeing that it is a phenomenon beyond man's experience, while, on the other hand, everything within the universe points to God's unlimited creative power"
I.e., in an earthquake.
This allusion to unpredictable geological and cosmic occurrences - earthquakes, the fall of meteors and meteorites, cosmic rays, and so forth - reinforces the statement about "how little of the sky and the earth ties open before them, and how much is hidden from them", and contrasts man's insignificance with God's omniscience and almightiness.
See last sentence of 24:31 and the corresponding note 41.