Firmament (Gen 1:6) (jumping ahead to the concept of firmament to provide context for v.2)
6 ¶ And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.
Hebrew Cosmology diagram. See also here or here.
The root of "firmament" means "hammer out", implies a horizontal area [UC 31]
Mesopotamian mythology shows after Marduk (or other various deities
from other times/places) vanquished Tiamat, goddess of the world-ocean,
depicted as a great sea-monster and other monster-like creations she
made to help her in her combat. After he had slain his chief enemy, he
cut her carcass horizontally, dividing it into two halves, one on top
of the other, and out of the upper half, he formed the heavens, and out
of the lower half, the earth, including the sea/"deep." [UC 32-33,
49-50]
From the Babylonian account of creation (Tablet IV, 137-140):
Genesis recognizes the Canaanite myth, but refutes it. No weapons, no carved body or segments, just physical unfolding taking the place of the mythical train of events