Welcome to Planet Earth
Welcome to Planet Earth , the third planet from a star named the Sun . The Earth is shaped like a sphere and composed mostly of rock . Over 70 percent of the Earth's surface is water . The planet has a relatively thin atmosphere composed mostly of nitrogen and oxygen . Earth has a single large Moon which is about 1/4 of its diameter and, from the planet's surface, is seen to have almost exactly the same angular size as the Sun . With its abundance of liquid water , Earth supports a large variety of life forms , including potentially intelligent species such as dolphins and humans . Please enjoy your stay on Planet Earth.