This question already has an answer here:
It's a fantasy setting, and the world is crazy, but has anyone tried to science it? Weather patterns that are unstable only around what are essentially the Equator and the Greenwich, that change frequently; chunks of just land hanging around in the middle of the sky; people who "kick the air" so hard that they can run in it; vast ranges in size for all creatures without apparent health issues; feats of superhuman strength from human beings. All that stuff's normal for them. Why?
What's so different about their planet that this works? The atmosphere? Gravity? The number of moons?
The question is specifically asking about the physics behind:
What gravity/atmosphere would be needed to allow chunks of land to float inside a planet's lower atmosphere?
And by float, I mean staying at a set distance from the surface for 400+ years without destroying life on the surface.