Earth is the planet on which we live. The planet was formed by a big dust- and gascloud. The particals in the cloud drew eachother with their gravity. Eventually the particals formed a liquid ball. The lightest materials came to the surface of the planet, cooled down and formed the earth's crust, which is divided into several layers:
 0-40 km depth is the earth's crust. Then from 40-400 km lies the upper mantle. Under the upper mantle lies the transition region (400-650 km).
Then, from 650-2700 km, the lower mantle, followed by D' ' layer from 2700-2890 km depth. This is where the core starts. First there is the outer core from 2890-5150 km, then the inner core from 5150-6378 km.

The inner core and the crust are solid, the outer core and mantles are semi-fluid. The core is probably composed mostly of iron (or nickel/iron) though it is possible that some lighter elements may be present, too. Temperatures at the center of the core may be as high as 7500 K, hotter than the surface of the Sun. The lower mantle is probably mostly silicon, magnesium and oxygen with some iron, calcium and aluminum. The upper mantle is mostly olivene and pyroxene (iron/magnesium silicates), calcium and aluminum. The crust is primarily quartz (silicon dioxide) and other silicates like feldspar.

The earth has a diameter of 12,756 km (7928 miles).
It takes our planet 365 days to rotate round the sun, 23 hours and 56 minutes to rotate round it's own axis. The distance from the earth to the sun is 149.6 million km (93 million miles). Earth's mass is 5.9736e24 kg.

The earth has one moon, which is called "the moon".
The moon is 81 times smaller then the earth and therefor has a very weak gravity. Because of this weak gravity, the moon doesn't have an atmosphere.
The moon rotates round the earth in 27 days. It influences the oceans on earth. The gravity of the moon gives us the tides.

Some pictures of the earth and the moon (click to see the large picture):