Doctor Who: Orphan 55

The part that really did not make any sense to me was that we already have life forms that thrive on CO2 rich atmospheres -- plants. So the fact that prokaryotes were not the dominant life form in this episode as they were at the beginning of the Earth, when the composition of CO2 was similar, made no sense to me at all. The planet was deemed "uninhabitable," just because humans and other animals could not survive there. How oxygen-breathing-centric.

Side note: entirely possible to create a drinking game with the number of times Vilma (Julia Elizabeth Fogel) says, "Benny!".