Blue Marble Earth

Explanation: 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 featured picture of Earth, dubbed The 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 human s. Please enjoy your stay on planet Earth.