the morals of an Atheist

i would like to ask a question if there is no god how can one tell right from wrong? i personaly belive in christanity but in all the relegeons they have a code of honor that must be followed by thoses of that faith now 'if' atheists are right imagen how civilization would have progesed with out the real or illitional gidence of a higher force would we still be where we are today or would have civilization fallin apprt cause of the greed of the people so once again...

 as an Atheist how can you tell right from wrong?