Etra Prime was the oldest planet in the known universe.
Etra Prime on a collision course with Archetryx. (DWM illustration of AUDIO: The Apocalypse Element)
The Daleks removed the planet from time and space so that they could mine the Apocalypse Element from the planet. Twenty years later the Daleks sent Etra Prime on a collision course with the planet Archetryx, which was hosting a temporal treaty attended by twenty of the Temporal Powers. (AUDIO: The Apocalypse Element)