Earth is a planet in the Solar System. Being the third planet from the sun, it's the only planet able to sustain life.
In the Series Edit
The entire book takes place on Earth with the exception of Chapter 10 and 15. However, all of the settings in the book do not exist. These include the following: Sunshine City, Timeville, and Wailua. Also, Ace, Roxy, and Will Guy are all supposedly born on this planet. They seem to be the only heroes who dwell in America or the world. But it is amazing that no one on Earth has noticed Timeville and it's existence.