Earth is the third planet from the Sun , and the densest and fifth-largest of the eight planets in the Solar System . It is also the largest of the Solar System's four terrestrial planets . It is sometimes referred to as the world or the Blue Planet. [ 22 ] Earth formed approximately 4.54 billion years ago, and life appeared on its surface within one billion years. [ 23 ] Earth's biosphere then significantly altered the atmospheric and other basic physical conditions, which enabled the proliferation of organisms as well as the formation of the ozone layer , which together with Earth's magnetic field blocked harmful solar radiation , and permitted formerly ocean-confined life to move safely to land. [ 24 ] The physical properties of the Earth , as well as its geological history and orbit, have allowed life to persist.
Journey To The Hollow Earth