The Mukhya Upaniṣads

Aitareya · Adhyāya 1 · Khaṇḍa 1 · The Waking of the Self into Worlds and Person

Passage 2

स इमाँल्लोकानसृजत ।अम्भो मरीचीर्मरमापोऽम्भः परेण दिवं द्यौः प्रतिष्ठाऽन्तरिक्षं मरीचयः ।पृथिवी मरो या अधस्तात्ता आपः ॥ २ ॥

In plain words

He created these worlds: the celestial waters, the shining rays, the mortal realm, and the nether waters. Beyond the sky lies the heaven called 'the waters'; the sky itself is its foundation. The rays are the intermediate space. The earth is the mortal region; and what lies beneath it — those are the waters.