If there is a stable wormhole orbiting Earth and the Aliens have the technical capability to collapse and otherwise manipulate said wormhole then they will have a fairly potent level of technology at their disposal. They could attack Earth by directing a large asteroid through the wormhole, once it comes out our end it will fall to Earth and cause good old fashioned destruction. . If you want to destroy the Earth all together and the aliens are advanced enough, perhaps they captured a neutron star and directed it through the wormhole. one of those bad boys materializing 400km above the Earth is going to cause an insane amount of devastation, The tidal forces would likely shred Earth. How long it would take I suppose would depend on what direction the Star was heading when it exited the wormhole and how fast it was going. If its directed straight at the planet then I suppose life on Earth would have a few seconds to realize the end was there. The star would punch through Earth like a bullet and the resulting gravitational forces would shred and suck a good deal of the matter onto the Star's surface. Anyone on the moon would be in for a bad day too, at the very least it would be slung off into the solar system and the colonists would slowly starve to death or freeze as power ran out. That is assuming the habitat wasn't shattered by the gravity of the passing neutron star.
If you go the nutron star route, nothing in the solar system is going to be left unschathed. Even Colonies on the outer planets are going to be effected as the nutron star will have a mass greater then the Sun so all orbits in the solar system will be disrupted. Basically its end game for everyone in the sol system unless they get very creative.
PS. come to think about it, No one on the moon would likely survive the nutron star's impact with Earth as the impact would release a tremendous burst of radiation that would probably cook everyone on the moon.
Happy thoughts.