The "soft reboot" of the UNIT era is pretty obvious, but every now and then i ponder that era when Doctor Who all but cut ties with Earth.
The Aliens Have the TARDIS 1977-1984
23 Oct 1976 - Sarah Jane leaves, end of Hand of Fear
(November: Doctor on Gallifrey, The Deadly Assassin)
1 Jan 1977 - Doctor meets Leela in Face of Evil. She might be human (?), but her people settled on another planet long ago.
1 Oct they pick up a tin dog (K9)
11 March 1978 - Leela leaves at end of Invasion of Time. Bye-bye, human.
2 Sep 1978 - Romana I joins Doctor and K9 for season 16. As with Leela, they visit Earth a few times, but most adventures are on alien planets.
Half of S18 is in a pocket universe. They pick up Adric 25 Oct 1980.
24 Jan 1981 - Romana and K9 Mark ii stay behind in e-space.
28 Feb 1981 - Tegan enters TARDIS in part one of Logopolis, final story of S18.
2 March 1984 Turlough leaves at end of Planet of Fire, S21. Last alien companion.
So that's... four and a half years in which none of the Doctor Who regulars are from Earth, and for three of those years, it's 2-3 aliens and a tin dog.
Then, during the Fifth Doctor's run, Tegan is the only human in a crew with 2-3 aliens, except near the end when she's replaced by Peri. The Fifth Doctor can't make it through a single story with a human companion before he croaks.
All together, that's seven years of the Doctor traveling with at least one non-human companion (including K9).
