In "The Hitchhiker's Guide to the Galaxy," Arthur Dent has trouble getting his mind around the Vogon Constructor Fleet's destruction of the Earth. He can't process it -- it's just too big. Arthur tries to narrow it down, but thinking of England, New York, Bogart movies and the dollar produces no reaction. Only when he considers the extinction of McDonald's hamburgers does it finally sink in.


Image courtesy NASA
The Earth, as seen from the moon. See more pictures of planets.
After deciding to write about how the Earth works, we felt a little like Arthur Dent. Even though it's tiny compared to the rest of the universe, the Earth is enormous, and it's extremely complex.

But instead of collectively going out for a burger, we decided to take another approach. Rather than examining each of the Earth's parts, we'll look at what ties it all together. Just about everything on Earth happens because of the presence of the sun. You'll get a basic idea of how vital the sun is to life on Earth and the wide variety of roles it plays in the next section.

Video Gallery: The Earth and Earth Day
Ever wondered whether events in space could destroy the Earth? Check out these original HowStuffWorks videos on whether solar flares or black holes could wipe out our planet.

In 2007, HowStuffWorks visited colleges and universities to talk about science, the Earth and conservation. We asked questions, students answered, and we offered our own explanations. Check out some of the conversations we had at Earth Day events around the country: