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 . The above picture of Earth, dubbed Blue Marble , was taken from Apollo 17 in 1972 and features Africa and Antarctica. It is thought to be one of the most widely distributed photographs of any kind. Earth has a single large Moon that 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.
Media Credits & Attribution
Credit: Apollo 17 Crew , NASA