In Turn Left we see what the world would be like if Donna never met the Doctor and he perished beating the Racnoss.
In this timeline, we cryptically see Rose all over the place using the companions to prevent the other earthly disasters before the final disaster comes in the blotting out of the stars. Which Rose explains is happening to all the other parallel universes.
We learn by the end of the season this was caused by the Dalek's Crucible, using Davros' Reality Bomb.
However, in order for the Crucible to work in the first place, the Earth must be present in the "Planetary engine" alignment. During Donna's alternate reality the Earth wasn't taken for this purpose and merely witnessed as the end came about, before Donna shattered that reality and went back to the true reality.
The question then becomes, how could the Dalek's accomplish this in this reality if the Earth is still in place?