Mosaic: 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 . This 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. Here , the world famous image has been recast as a spectacular photomosaic using over 5,000 archived images of Earth and space. 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.