The Earth is a planet of the solar system, the third one starting from the sun. It is the largest telluric planet and densest planet of the solar system. It was formed 4.57 billion years ago and has one natural satellite, the Moon. It is also the only planet of the universe known to humans to support life. The surface of the planet is made up of about 71% of water; the 39% left or so are the continents and islands.