It has taken me 3 viewings, but I think I have discovered why the Decepticons arose from under the surface of the moon. Sam had discovered from the Russian men that the Decepticons raided the Ark and took hundreds of pillars. They probably stayed on the moon after they raided the ship and were told that when the space bridge is activated, to enter it to go to earth. Other things I noticed were that it looks like the footage of Optimus vs. Shockwave in the Burger King commercial is almost identical to the Optimus vs. Sentinel fight. So, it looks like they just switched out the different characters. Also, in the 3D version, Shockwave changes color in almost every scene. In some scenes he looks pure purple and in others, he looks blackish silver. I've heard that in 2D, he looks purple throughout.