Christine and Eva both talk about everyone suffocating if the surface of the dome calcifies. They say this in the middle of a forest full of trees, which produce oxygen, eventually lack of sunlight would cause the trees to die, but it's more likely that the group would run out of food, since they wouldn't be able to grow crops, long before they suffocated.
When Joe radios to Julia that he and Norrie have obtained the schematic, the next thing he says is, "Copy that," as if responding to something said at the other end. If there was a communicated line there, it was cut.