SB 4.17.21
mam vipatyajaram navam
yatra visvam pratisthitam
atmanam ca prajas cemah
katham ambhasi dhasyasi
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The cow-shaped earth continued: My dear King, I am just like a strong boat, and all the paraphernalia of the world is standing upon me. If you break me to pieces, how can you protect yourself and your subjects from drowning?
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Beneath the entire planetary system is the garbha water. Lord Visnu lies on this garbha water, and from His abdomen a lotus stem grows, and all the planets within the universe are floating in the air, being supported by this lotus stem. If a planet is destroyed, it must fall into the water of garbha. The earth therefore warned King Prthu that he could gain nothing by destroying her. Indeed, how would he protect himself and his citizens from drowning in the garbha water? In other words, outer space may be compared to an ocean of air, and each and every planet is floating on it just as a boat or island floats on the ocean. Sometimes planets are called dvipa, or islands, and sometimes they are called boats. Thus the cosmic manifestation is partially explained in this reference by the cow-shaped earth.