The whole Genesis planet idea doesn't even stand up to much thought. A device that was designed to be fired at an existing planet and terraform it somehow explodes on a starship in the middle of a nebula and manages to form a planet from scratch. None of it actually makes any sense.I assume it turned into a formless lump of stem cells which was the raw material to quickly grow baby Spock. Then the Genesis energy field provides his body with the energy needed to grow, no food needed. The big microbes probably ate anything left over. We really aren't supposed to think about it this hard, the idea starts to fall apart.