system
Given the following post, respond as if you're commenting on Reddit:
human
[Monsterverse] Simply put, what is the "Hollow Earth"?
gpt
Hollow Earth is an old theory - dating back at least to the late 1600s. Basically the idea is instead of our planet being a solid ball of rock and metal with a molten core, it's more like an eggshell. Exactly what's inside depends on who's proposing the idea, sometimes it's hollow with a star or two inside for light, sometimes there's concentric smaller shells.