Doctor Who Series 12: 10 Huge Questions After Orphan 55
4. Haven't We Already Seen The Earth Destroyed In Doctor Who?
Yes, in the standard timeline of Doctor Who, the one in which Ryan, Yaz, Graham and most, if not all, of the Doctor’s other former companions have lived through, the Earth’s final destruction takes place in the year 5 billion. Despite the horrors that humanity and other alien species inflict on the planet, it survived until the sun became a red giant (The End of the World). The human race would continue by planetary resettlement, but Earth was vacated when its fate became clear.
There have been various other end of the world or dystopian scenarios played out, some of which are from alternative or aborted timelines, such as the chemical wasteland occupied by the zombie-like Haemovores (The Curse of Fenric) to destruction at the hands of the Master (The TV Movie). Usually, the Doctor will do something to change the course of history or to put the Earth back on its rightful trajectory (literally so in Journey’s End).
The Doctor is keen to reassure her friends that Orphan 55 is just one future among many, but this is one occasion where she does nothing to directly prevent it from happening in the first place. It is still possible to tie Orphan 55 into the standard timeline. Perhaps the very same Earth that Rose and the ninth Doctor watched explode had become an orphan planet long before then.