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.

By what means is sin made known?
How highly does God regard obedience?
What is said of his mother and his grandmother?
What power has claimed authority to change the law of God?
Will the world be prepared to meet Him?
Concerning what did Christ tell us not to marvel?
How was Christ strengthened after His forty days' fast and temptation in the wilderness?

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