The Source (The Doctor's Daughter)

The "Source" was the name given to the terraforming device used in the colonisation effort of Messaline. Over the time that the Human and Hath colonists fought each other, the Source's true purpose had been forgotten. The Humans, at least, believed that it was the "Breath of Life", breathed by the Creator at the beginning of time. The two races also believed that it had the power to destroy the race opposing the one who held it.

It was destroyed by the Doctor to show the two races the true purpose of the Source and the reason they were actually on the planet. (DW: The Doctor's Daughter)