why is the Earth called "Earth"?

Answer 1

The official names of planets and their moons are governed by an organization called the International Astronomical Union (IAU). The IAU was established in 1919. Its mission is "to promote and safeguard the science of astronomy in all its aspects through international cooperation". Its individual members are professional astronomers from all over the World. The IAU is the internationally recognized authority for assigning names to celestial bodies and any surface features on them.
The IAU recognizes that astronomy is an old science and many of its names come from long-standing traditions and/or are founded in history. For many of the names of the objects in the solar system, this is especially so. Most of the objects in our solar system received names long ago based on Greek or Roman mythology. The IAU has therefore adopted this tradition in its rules for naming certain types of objects in the solar system.
Earth is the only planet whose English name does not derive from Greek/Roman mythology. The name derives from Old English and Germanic. There are, of course, many other names for our planet in other languages.
http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question48.html

Answer 2

It is made of dirt, which is called earth. If you ask me, it would make more sense to call it "ocean" or "water" than earth...but whtever.

Answer 3

Because primitive people didn't realize they were living on a planet, so they just called what was under their feet "dirt", and the name stuck.

Answer 4

Why not?
Its called earth because it is not called anything else.
Why is your name what it is? Same answer.

Answer 5

Instead of what? Gaia? Terra?