Earth

Earth is a blue and green planet home to most of the characters in the comic.

Beginnings
Earth would start out almost identical to our Earth, with the diverging point being sometime in the late 21st century, when Selene's interference caused the annihilation of almost all life on the planet. The remaining toxic waste would mutate creatures, causing some odd forms of life to propagate. Most of the satellites around Earth would burn up in the atmosphere without humans.

Migration of Celestians
A rift between ancient Celestine and Earth would open at some point, causing some of them to start living on Earth, where the modern "booksona" species would evolve from. Some artifacts in the planet would bestow some of them with magic, granting some books elemental abilities. At some point, some would evolve to adapt to underwater, creating a underwater society named Aquarius.

Modern Times
About a million years after the war that would kill most life, some archeologists like Amber and Ranger would start looking for remains of the past. Percy, an older book, would even open a museum at one point to show the artifacts. An intelligent turtle named Geoffrey Sr would found a tech/gaming/shipping company that would quickly bring technology to the mostly still primitive world. Some forms of government would pop up, but places like Mallardia remain without a central government.

Trivia

 * It's strongly implied the event that caused the destruction of the humans was a war between the USA and Russia.
 * Deseret, Mallardia, and Arcticoura remain the main established areas of the planet, with most other areas remaining unexplored.
 * Earth Duck, although vaguely resembling Earth, seems to be able to transport people to the rough corresponding areas on the globe. The reason for this is unknown.