Allah, ta^ala, did not create all the creations at one time. Had He willed for this, it would have occurred. Rather, in six days, He created the heavens and Earth; and for Earth Allah created rivers, mountains, and valleys. The wisdom of this is to teach us not to be hasty in doing things.

The first creation is water. The Prophet, sallallahu ^alayhi wa sallam, said:

إِنَّ اللهَ تَعَالَى خَلَقَ كُلَّ شَيْءٍ مِنَ الْمَاءِ

Innallaha ta^ala khalaqa kulla shay’im minal-ma’.

Which means: “Allah created everything from water.” (Related by Ibn Hibban.)