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.

What question did the eunuch ask after Philip had preached Jesus unto him?
What will be the fate of those who do not obey the gospel of Christ?
What did Daniel ask of one of the heavenly attendants who stood by him in his dream?
6. Until what time were the saints, times, and law of the Most High to be given into the hands of the little horn?
Under the old covenant, what did the people promise?
How did Elijah pray before obtaining his request?
What will be excluded from this city?

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