"Below us, blue and white and so beautiful it brought tears to your eyes, was Earth. Sun sparkled off the ocean. Clouds swirled over the Gulf of Mexico, a big spiral, maybe a hurricane. [...] We looked. Through the eyes of the animals of Earth, but with the minds of human beings, we looked down at our planet. Our planet."

Earth is the planet inhabited by, most notably, Humans, Nartec, and eventually later, Hork-Bajir, Taxxons, Yeerks and Andalites.. It is the current target for the Yeerks who wish to enslave the human race. Elfangor lived on this planet with Loren in a different dimension using the Time Matrix. The Ellimist reversed the effects of this after Elfangor had a child with Loren that he found out about after time was returned to normal. The child, (Tobias) later became an Animorph to fight for Earth. Please see Wikipedia's real life earth page.

Yeerk InvasionEdit

"So many species on this planet. So many balances and connections. Everything preying on everything else. Every power is checked by some other power. Every advantage is canceled by some disadvantage."
"Yeah. Earth. It's a tough neighborhood."
"When we take this planet, we will eliminate these species. We will simplify. Things should be simpler. Yes, much simpler. [...] This is a savage planet. We will tame this world, when we take it over."
Temrash 114 to Jake[src]

To be added