Continuity mistake: When the Doctor, being held by two of the crewmen, explains that there's a geographical anomaly the sub can land on to halt its descent, the hand of the crewman holding his right arm disappears in a close-up, followed by the crewman himself disappearing in the next shot. (00:04:57)
Continuity mistake: When Skaldak grabs Professor Grisenko's head and announces that Martian law decrees the destruction of the Earth, his hands change position on Grisenko's head between shots. (00:31:47)
Continuity mistake: The submarine surfaces among icebergs at the end. Just as the others go back into the submarine, the Doctor stays up there. Some snow goes onto his lip and his hair. In the following shot, we can see he isn't moving. But in the next shot, the snow on his hair and lip isn't there anymore. (00:40:00)
Factual error: The rank insignia of the Soviet officers is completely inaccurate. The captain wears the epaulets of a captain first rank (captain) and the sleeve insignia of a captain second rank (commander). Lieutenant Stephashin wears the epaulets of a senior lieutenant and the sleeve insignia of a captain third rank (lieutenant-commander). The third officer wears the epaulets of a captain second rank and the sleeve insignia of a captain third rank.
Chosen answer: 1) When Stephen Moffat took over he ignored a lot of what had been developed before (there is not in-universe answer). 2) It would have killed Rose, so the Doctor absorbed the energy. His body regenerated before the energy could do a significant amount of damage that would prevent regeneration.