Earth, also known as “the Earth” and “the World” and sometimes referred to as the “Blue Planet”,[24] the “Blue Marble”, Terra or “Gaia”, is the third-closest planet to the Sun, the densest planet in the Solar System, the largest of the Solar System’s four terrestrial planets and the only celestial body known to accommodate life. It is home to millions of species,[25] including a global population of humans,[26] that are supported and nourished by its biosphere and minerals. The human population is grouped into around two-hundred independent sovereign states that interact, among other means, through diplomacy, conflict, travel, trade and media.