The Eye of Harmony on Gallifrey is mentioned in the episode as being the power source of the TARDIS, as it is in a number of earlier series, particularly The Deadly Assassin (1976) and the TV Movie (1996).
Pump Up The Volume
The new console in the TARDIS includes what looks like a bicycle-pump mechanism; this was subsequently identified as a Vortex Loop in Attack of the Graske (2005).
Lost In Translation
The Time Lord gift concept, which explains Rose's ability to understand and be understood by the aliens was one first introduced by the Fourth Doctor in The Masque of Mandragora (1976).
The Supercharged communications device concept first appeared in episode The Three Doctors (1972-73).
This isn't the first time in the shows history that the Earth has been burned by the Sun. Other episodes include The Ark In Space (1975), The Mysterious Planet (1986) and The Ark (1966).
That Sinking Feeling
The Doctor drops another hint that he was on the (real) RMS Titanic when it sank, when he tells Jabe of an incident when he had to cling to an Iceberg the last time he was on an unsinkable ship. He has previously been associated with the doomed ship in Rose, The Invasion Of Time (1978) and the novel The Left-Handed Hummingbird.
Back To The Future
The last time the Doctor visited the 22nd Century in the TARDIS (2164 to be precise) was in the adventure The Dalek Invasion of Earth (1964).
Zoë Wanamaker makes her Doctor Who debut as the voice of CGI creation Cassandra. She later appears onscreen in Series Two's New Earth.
According to writer Russell T. Davies, Cassandra and her drastic beauty treatments were inspired by various female celebrities at the Oscars.