One rotation is call a day. So one day is 24 hours. Earth is a little over 12800 kilometres in diameter, and about 39000 kilometres around the equator. On a size basis, the Earth is right in the middle of the planetary family, with four planets, Pluto , Mercury , Venus and Mars , being smaller, and four planets, Jupiter , Saturn , Uranus and Neptune , being larger. Earth seems to be very unusual.
Earth has a core, or center, that is solid and made up mostly of iron.
The large amount of iron is what creates the magnetic field that makes compasses work. On top of the solid core is a very thick layer of molten, or liquid, rock. On top of the mantle is the solid layer that makes up the continents and the ocean floors. This is actually very thin, averaging less than 50 kilometres thick. Surrounding the solid surface are layers of atmosphere.