When Krypton exlpoded it was due to a Radioactive chain reaction in the planet's Uranium core and it irradiated the shards of the planet that survived creating Green Kryptonite (The other colors came from the Green being exposed to various elements and cosmic activities while bound for earth) and Green Kryptonite is poisonous to everything if exposed to it long enough (such as Lex Luthor contracting cancer from his Kryptonite ring he wore for many many years) but Superman's Kryptonian cells allow him to absorb more yellow sunlight than a human (more like a plant) and enhance his abilities, so it probably works the same way for Kryptonite by accelerating the effect on him and all other Kryptonians like Zod, and Kara (Supergirl).
Edited: tyrel on 30th Nov, 2007 - 7:12am
Krypton Rock So Powerful?
I have always wondered why Superman never used super speed or even strength to leap out of a room with Kryptonite. Is Kryptonite so disabling of Superman's powers? If so we need to know what is the factor of distance to rock and effect.
I think the answer to that is straight theatrics. As it does seem to take time when he is exposed to become weak to the point he can not move. Fear might also be a possible factor in that. He becomes petrified by the one thing that truly can harm him. I am thinking on the lines of a sever phobia. It over takes his senses and he is suddenly in a very dark scary place that prevent him from taking action.
After all if you know that nothing can hurt you then a simple rock turns you weaker then a baby it surely would have some emotion and mental issues attached to the item.
A phobia, that is an interesting reason. I wonder if his father purposely made the rock his weakness. After all if a human scientist working with limited technology could make it Lana's power then why didn't it be the same for Superman?