Heaven and Earth are praised as a pair: wise parents whose sons are the gods (1.159), two bowls between which the Sun travels, a bull and a spotted cow, made by the most skilful of the gods and set on pillars (1.160). Hymn 1.185 opens by asking which is elder and how they were born, says the footless pair bear footed offspring, and repeats a plea for protection through seven verses. 6.70 says they stand parted by Varuna's decree and drip with honey and fatness. 6.51.5 addresses Father Heaven and Mother Earth directly.
The two worlds were once together and then went apart. No rain fell and there was no heat, and the five peoples were not in harmony. The gods brought the two together and they performed the divine marriage. The earth quickens the sky with smoke and the sky quickens the earth with rain. The earth placed in the sky the place of sacrifice, seen as the dark in the moon; the sky placed salt in the earth, which is why herdsmen ask whether a pasture has salt.
What is different here:
Turns the timeless pair into an event: a parting, a drought and a remarriage arranged by the gods, with exchanged gifts. The Rigveda hymns have no parting story; they only say the two stand apart.
In the Atharvaveda's wedding verses the groom tells the bride that he is the heaven and she is the earth, and that they will live together as parents of children to come. The first couple is used as the model for a human marriage.
What is different here:
Not a narrative: Heaven and Earth appear only as the pattern of husband and wife in a marriage verse.
Sources: Hymns of the Rigveda, tr. R. T. H. Griffith (1896), hymns read for the Vedic layer; Rigveda Brahmanas: the Aitareya and Kausitaki Brahmanas, tr. A. B. Keith (1920); Hymns of the Atharva-Veda, tr. R. T. H. Griffith (1895)