A Level 5 planet, also called a level 5 civilization, was a designation used by Galactic Law in reference to certain worlds, with the implication that it referred to relatively primitive planets not yet fully integrated into galactic civilisation. Level 5 planets were protected by various Galactic Laws. (TV: Smith and Jones, Partners in Crime, The Eleventh Hour)
Earth is a Level 5 planet. (TV: Voyage of the Damned)
While a level 2 planet in the 1940s, (PROSE: Ghosts of India) Earth became a level 5 civilization by 1957, (PROSE: First Frontier) remaining at that status through 1979, (TV: City of Death) 2008, (TV: Voyage of the Damned, Revenge of the Slitheen, The Eleventh Hour) 2009, (TV: Partners in Crime) and into and 2040. (AUDIO: Phantoms of the Deep) However, Romana I once referred to Earth in 2011 as a level 4 civilization. (AUDIO: Ferril's Folly)