"Exponentially small" here means "the probability could be ~ e^-n" where n is a number proportional to the complexity of the minimal evolving system. This would happen if there's some gap that has to be bridged by random chance before we get a system capable of sustaining natural selection.
The point here is that this could easily be vastly smaller than 1/N, where N is (say) the number of atoms in the universe x age of the universe x rate at which atoms might interact to form such systems.
I think you could have easily understood this point if you had made an effort to do so, without me having to spoonfeed it to you here.
