How early was this sacrificial system known?

Answer

"By faith Abel offered unto God a more excellent sacrifice than Cain, by which he obtained witness that he
was righteous, God testifying of his gifts." Heb. 11: 4. See Gen. 4: 3-5; 8: 20.

How is eternal life bestowed?
For what did Christ, just before His ascension, tell His disciples to wait?
What will be the standard in the judgment?
18. Does Christ anywhere in the Scriptures ever claim any other day of the week than the seventh as His?
What are all admonished to do when these signs have appeared?
Did angels exist before the death of any of the human family?
What will follow this great conflagration?

Questions & Answers are from the book Bible Readings for the Home Circle