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 writings are specifically mentioned as containing some things difficult to understand?
What gave special force to the oath of an angel?
Into what condition has sin brought the entire creation?
What different results attend the covering and the confessing of sins?
What will sound doctrine enable the faithful teacher to do?
How should the truth ever be cherished?
How had Moses spoken of another and greater dispersion?

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