whole movie was kinda stupid .... i mean seriously .... his evil plan was to make more land .... how absurd
and the reason why he could do it was, it wasn't made of pure kryptonite .... or else he would've died instantly when he stepped on that thing, but the time it took to take affect was a bit actually .... and he actually hadn't exposed to much sun before going on it .... but then he flies into the sky after being rescued and absorbs more sun n goes full power .... and basically he lifts the thing up n into space before it starts affecting him hardcore (and also not sure if kryptonite's effects gets reduced under water)
but yeah .... whole **** was stupid