Original sin is indeed not mentioned in Scripture. Some concepts that many people think are Christian such as the Trinity and the original sin, only became Christian doctrine for political reasons after the council of Nicea. Jesus never said anything of original sin. He would probably have been dismayed by such an idea.
Rom 5:12 Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
Rom 5:13 (For until the law sin was in the world: but sin is not imputed when there is no law.
Rom 5:14 Nevertheless death reigned from Adam to Moses, even over them that had not sinned after the similitude of Adam's transgression, who is the figure of him that was to come.
That simply means what it says. Adam was the first sinner and all other men also have sinned, and thus we are doomed to death even when our sin was not similar to Adams, which was disobedience. We are punished not for Adams but for our own sins of course.
Jesus also was not sacrificed for Adams sin, he was sacrificed for all peoples sins even when they are not Christian, and even for extraterrestrials.
