Earth is third planet from the Sun. It is the home planet of humanity and the Titans.
Millenia ago, before the evolution of mankind, Earth was dominated by hundreds of super-species. In the past, King Ghidorah, an extraterrestrial three headed dragon invaded the planet and attempted to destroy and terraform the planet by enslaving the Titans into doing his bidding. His reputation as an alpha caused him to clash with Godzilla and Mothra for supremacy over the Titans and the planet itself. He and Godzilla clashed for centuries until the former was defeated and sealed off in ice for millennia to come. At some point in time, the majority of the Titans died off or went into hibernation, with Dagon, Godzilla, MUTO Prime and King Ghidorah being notable examples.