people keep saying that MoS lacks the green rock but thats because the rock isn't green or even a rock at all. i think that kryptonite is the kryptonian atmosphere. Clark's body has adapted to earth's atmosphere. and the kryptonian air is lethal to him. and the argument can be made that it can't be turned into the kryptonite we all know and love, but think about this for a second: aire can be liquefied and liquids can be solidified. and in the sequel we know that it is highly likely for two of the world's greatest minds to be present. it'd be crazy for one to not assume that one of the two won't figure out a way to make it happen