Why was the "Earth" named Earth? Who named it? How have the planets been named?

Answer:
Who gave our planet the name Earth? Who named the other planets?
The official names of planets and their moons are governed by an organization called the International Astronomical Union (IAU).

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.

With the exception of Earth, all of the planets in our solar system have names from Greek or Roman mythology. This tradition was continued when Uranus, Neptune, and Pluto were discovered in more modern times.

Mercury is the god of commerce, travel and thievery in Roman mythology. The planet probably received this name because it moves so quickly across the sky.

Venus is the Roman goddess of love and beauty. The planet is aptly named since it makes a beautiful sight in the sky, with only the Sun and the Moon being brighter.

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.

Mars is the Roman god of War. The planet probably got this name due to its red color.
Jupiter was the King of the Gods in Roman mythology, making the name a good choice for what is by far the largest planet in our solar system.

Saturn is the Roman god of agriculture.

Uranus is the ancient Greek deity of the Heavens, the earliest supreme god.
Neptune, was the Roman god of the Sea. Given the beautiful blue color of this planet, the name is an excellent choice!

Pluto is the Roman god of the underworld in Roman mythology. Perhaps the planet received this name because it's so far from the Sun that it is in perpetual darkness.