Environmental Story: Adventure Time

The Land of Ooo is the main setting of Adventure Time, and is the home continent of Finn and Jake, along with all of their friends and foes. It is divided into many different kingdoms, of which the most prominent are the Ice Kingdom, Candy Kingdom, Castle Lemongrab, Wildberry Kingdom, Lumpy Space, Fire Kingdom, and Cloud Kingdom. There are also many geographical areas not known to be part of any kingdom, such as the Evil Forest and the Bad Lands.
Pendleton Ward, the creator of Adventure Time, has stated both in an interview[2] and in his FAQ page[3] that the Land of Ooo is actually a post-apocalyptic Earth, the result of a global disaster called the Mushroom War, hence the ruined pieces of modern technology scattered across the land.

It is possible that Finn may be the sole human being left in Ooo. It is also possible that the Mushroom War is responsible for killing off all the other humans, or that they mutated into the current and varied inhabitants of the planet. In "Her Parents," Lady Rainicorn's parents mention that they wanted to eat Finn because they never thought they would get the chance to eat an actual human, implying they are either extremely rare or extinct.
The Lead Designer of adventure time said that the creators set a high bar for the design of the animation, the characters, the environment, how ever made up or non-sense it might seem al the design details have to make sense, and they're very careful with the world they are  trying to create, in order to tell the story effectively