A planet (from Greek πλανήτης, a derivative of the word πλάνης meaning "moving"), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.[a][1][2]
Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune are all planets. If a rock is massive enough, it will become round under its own gravity. Many of the planets are less massive than the earth, and they are still round. (in FET, maybe ALL the planets are less massive than the earth) Therefore, the earth should have enough mass to be rounded by its own gravity. So it is a planet, and it is also round.
...unless the earth is made of some exotic matter which doesn't have gravity. So what separates the matter making up the planets and the matter making up the earth? Because there's some really good evidence everywhere that gravity exists here.