Gelezen (planet)

The planet of Gelezen for thousands of years had a self imposed isolationist policy that was maintained by a protective time-field that surrounded the planet. The barrier was destroyed by Martha Jones when she was taken to the planet using a long distance teleport beam that first detected her in London in the 1960s. Martha was chosen for her DNA that was enhanced by having travelled with the Doctor through time and was seen as a means of refreshing the corrupted human DNA material from which the Gelezens had become a clone race facing extinction. (DWAM: Signs of Life)