Earth in Animorphs
The latest target of the Yeerk Empire, Earth is also the home of the latest effort at resistance to it: the Animorphs. Formed when an Andalite spacecraft crashed into the construction site, where the five then-normal teenagers who would become the core group of Animorphs had decided to take what turned out to be an ill-conceived shortcut.
They were then introduced to both one of the greatest heroes, and one of the most depraved villains, that they would ever know; both in short order.
Earth in Guyver
The group or groups of aliens variously referred to as the Creators, the Advents, or Uranus, came to the planet an unspecified amount of time ago. Using their scientific knowledge, they shaped and influenced life on the planet, until they had created the precursors to the human race. Then, after they had settled on a base form, they begun to create the creatures that would come to be known as Zoanoids.
That task done, the Advents turned their attention to the creation of a general to command their legions of Zoanoid soldiers.
With their general and their troops, the Advents began making plans to create the other eleven Zoalords that they would use to command them, those who would serve under Alkanphel, and likely act to further enforce his will. However, none of this came to pass. The Advents, likely feeling quite confidant in the wake of their successfully completed experiment, decided to carry out another.
Equipping one of their symbiotic armors to a human host, intending to study the effects of such a combination, they created something that they had never seen before: the creature that they would come to call Guyver.
Earth in Transformers
The landing site of the Ark - in some canons - or for a group of Autobots - in others - Earth is often the focal point of Decepticon attention.