How did Job and Noah know that they should make sacrifices to God?

The sacrifice system was received after Exodus and is described in Leviticus. Also in Leviticus it is described what clean and unclean animals were. 1. How could Job and Noah know that they should be doing sacrifices and in Noah’s case what clean animals are(Genesis 8:20–21)? 2. How did Job know who the real(Jewish) God is, when he was not Jewish and God has not revealed his sacrificial commandments in Leviticus, yet? It seems to me that this is good evidence that Jews invented these stories and put their current understandings in them, not realizing that the people in the stories would not have known about their current Jewish laws. Argument from silence like "well, probably God did tell them somehow" is not a good argument.