Earth is the third planet from the Sun and is the largest of the terrestrial planets. All of the planets, except for Earth, were named after Greek and Roman gods and goddesses. However, the name Earth is a Germanic word, which simply means “the ground.” The Earth was formed approximately 4.54 billion years ago and is the only known planet to support life. Earth's atmosphere is made mostly of nitrogen and has plenty of oxygen for us to breathe. The atmosphere also protects us from incoming meteoroids, most of which break up before they can hit the surface.

Pop Culture

Storytellers explore the nature of our planet and possible alternate realities in many books, movies and television shows. The iconic Planet of the Apes film (and many sequels) takes place in a future in which astronauts "discover" a planet inhabited by highly intelligent apes and primitive humans, only to realize later, much to their dismay, that—spoiler alert!—it was Earth all along.

In the long-running and re-booted television series Battlestar Galactica, tired survivors of a war with highly evolved robots called cylons are on a quest to find Earth, a long-lost colony.

In other stories, Earth has been abandoned or destroyed, such as in the Joss Whedon series Firefly or the book and its film adaptation The Hitchhiker's Guide to the Galaxy. In the animated feature Titan A.E., Earth has been destroyed by an alien species, but a well-placed planet builder recreates it and all the species that live on it.