On a size basis, we are right in the middle of our planetary family, with four planets, Pluto, Mercury, Venus and Mars, being smaller, and four planets, Jupiter, Saturn, Uranus and Neptune, being larger. We only have one Moon and it has been an important part of our culture, literature and mythology since time began. The Moon is about one-fourth the size of Earth, with a diameter of a little over 2,000 miles. Earth is the only planet in the solar system that has solar eclipses, which happen when the Moon moves between the Earth and the Sun. Earth is the only planet that does not have a name from either Greek or Roman mythology.
Earth has a core, or center, that is solid and made up of mostly of iron.
The large amount of iron in our planet is what creates the magnetic field which compasses are based on to roughly determine North. On top of the solid core is a very thick layer of molten, or almost liquid, rock. The solid layer, or crust, that makes up the continents and the oceans is actually very thin, averaging less than thirty miles thick. The continents actually float around on this top layer, which is explained in Plate Tectonics of the geology of our planet.