Everyone wearing a GL ring was pulled into a different universe through the source wall, this hole was caused when Hal in a desperate moment during God Head decided to bring Black Hand to the source wall. Black Hand basically revived all the beings stuck on the source wall and let them go wild on New Genesis. Unfortunately they started becoming stone again after a while and Black Hand's hands were also turned to rock.
Somehow this mass revival left a hole in the source wall which sucked up every GL wearing a ring (why? We don't know). Meanwhile Hal was already hobo hal and using Krona's gauntlet which spared him of this (Soranik was given a yellow ring just in time as well because Sinestro's future seeing waifu told him the GLC would disappear). Black Hand with his new stone arms could now essentially petrify anything he touched much like what happens when someone touched the wall, the petrification spread like wildfire because petrified objects also caused petrification upon contact. Hal managed to capture Black Hand and took him to the source wall to try to fix things by chucking him in.
On the other side John and the GLC had just found the way back to their universe but it was suddenly closed, the only thing John saw was Hal on the other side, closing the rift. You see Hal had no clue the GLs fell through that hole and accidentally left them stranded. Eventually the corps found another way back and now they're here.