The hole in the Earth on the Adventure Time Earth is shown on almost every view of the Earth. The hole is a fictional event that is based on a direct cause from the Mushroom War. Some think that the Mushroom Bomb is the cause of this hole. Really, a comet hit the Earth. This is hinted in the episode, I Remember You on the picture frame in Ice King's time room. Also, in the episode Finn The Human, a comet is shown passing the Earth while Marceline is talking about what Simon Petrikov did to stop the Mushroom Bomb from hitting the Earth. The reason that the hole in the Earth is the cause of the Mushroom War is because in the episode Finn The Human the comet doesn't hit the earth. One bomb could not create that big of a hole, and, in addition, it would wipe out all of humanity and all living things if it was powerful enough to make that big of a hole- It would obliterate the world. Same with the comet, unless the world was frozen, or even part. If the world was frozen before the Mushroom Bomb went off, there would be no one to launch or drop the bomb. Therefore, the comet hit the Earth in a cause of the Great Mushroom War. The reasoning that the comet didn't hit the earth in the episode Finn The Human is either based on the Mushroom Bomb not exploding or the violent storms, tornadoes, earthquakes, and other natural disasters the Ice King's crown made after Simon Petrikov died from being crushed by the Mushroom Bomb. Based on the facts of physics, how powerful a nuke is, and what kind of damage a nuke can actually do (in realistic terms), narrows it down to that the Mushroom Bomb couldn't have been powerful enough to move the Earth off it's natural orbit. Now, we all know that the Mushroom Bomb wasn't just a nuke, but also was a way that released The Lich (character) into the world. So, in the actual Adventure Time reality, the comet was supposed to hit the earth. The comet was probably based on a meteor that was supposed to hit Earth in the early 21st century (In our real world). Since Simon Petrikov froze the Earth in order to try and preserve the human race, and other creatures, or that he turned into the Ice King and made the earth, or just part of it his Ice Kingdom, made it possible for mutants and other creatures to be preserved and protected from the blast of the comet and the lava splatter it made across the earth after impact. Since the Ice King, or Simon Petrikov, froze areas of the Earth and the creatures within thoes areas fast, made it possible for creatures to be able to be frozen without dying slowly from the cold, frost bite, etc. Therefore, they were able to be preserved, which make up some, but not all, of the Land of Ooo's main, minor, and extra characters.