Continuity mistake: In the beginning when the crew is in the jumper, Ronan Dex has his hair tied back. When they land on the island and walk into the camp, his hair is down, and then they have to run back to the jumper when the prisoners start shooting at them. When they get back in the jumper, Ronan's hair is tied up again.
Continuity mistake: In the scene where Michael is first introduced to his quarters, he goes to pick up a picture of his parents. In the first shot, the laptop next to the picture is closed, but in the next shot through the security camera, the laptop is wide open.
Continuity mistake: At the end of 2-2, Runner, Weir shows Ronon images of the destruction of his home world - a fact he had been unaware of. But in "Trinity," Ronon says "all these years I thought I was the only survivor."
Answer: Because even all 4 Naquadah generators (one was destroyed) together is only enough to dial Earth for approximately 1.2 seconds (As seen in the episode "Letter from Pegasus"). Further, if Earth had found a ZPM, they would dial Atlantis and let them know. After all, the SGC has no other use for a ZPM than to dial Atlantis.
Grumpy Scot