Zygor

Zygor was the home-planet of the Zygons. Zygor was known to be warmer then Earth and covered in water. This water was in the forms of lakes, which have a different mineral composition than those of Earth. There were also no icecaps on the planet. Known native lifeforms of Zygor include the unaltered Skarasen and the Zygons. The whole planet was destroyed in the war against the Xaranti, though many Zygons were able to escape before the destruction. (DW: Terror of the Zygons)

Two groups of Zygons attempted to make Earth more like Zygor; those that arrived in the 12th century (DW: Terror of the Zygons) and those that arrived in 1909. (TDA: Sting of the Zygons)


 * This would suggest that the destruction of Zygor probably occurred no later than 1909. Alternatively, they may have attempted to modify all of the planets they conquered.