I thought that the planet had some some sort of energy source at the core that provided the power to dial the 9th chevron, something that can't be done just anywhere.It was an evacuation, and he could have dialed anywhere other than Earth (pick a barren planet if you want). Obviously, the nine-chevron address can at least theoretically be dialed from somewhere else (as it was originally supposed to be dialed from Earth). It's not worth putting everybody's lives at risk (including a freaking Senator, dozens of civilians, and an IOA representative).