“Doctor Who and The Silurians” introduced for the first time a race that has continued to reappear throughout the show’s history right up until recent seasons: the Silurians, also referred to as Homo Reptilia, reptilian bipeds who sought safety underground from a potentially cataclysmic encounter with a planetoid (which became our moon, ending up orbiting rather than devastating our planet). Since then, while they were hibernating beneath the Earth, primates came to dominate.
The dispute over the Earth/ground, with one group now inhabiting it but another claiming that it was theirs long before, mirrors a variety of conflicts over patches of the planet, and so leads naturally to a discussion of how to address and settle such competing claims.
Liz Shaw’s role in the episode is important, and several news outlets reported the fact that the actress who played the role, Caroline John, recently passed away. IO9 credits her with helping to save Doctor Who.
The episode also features the Doctor as scientist, trying to find a cure for an epidemic – something that each of the first three Doctors did at some point.