Replies

“Christ wasn't around at the time of Cain and Abel.”
John 1:1 “In the beginning was the Word, and the Word was with God, and the Word was God. 2. He was in the beginning with God 3. All things came into being by Him, and apart from Him nothing came into being has come into being. 4. In Him was life, and the life was the light of men.”

John 1:1 “What was from the beginning, what we have heard, what we have seen with our eyes, what we have beheld and our hands handled concerning the Word of Life— 2. and the life was manifested to us—3. what we have seen and heard we proclaim to you also, that you may have fellowship with us; and indeed our fellowship is with the Father, and with His Son Jesus Christ.”

“Was Abel a martyr? I don't think Cain killed him for his religious beliefs.”
Hebrews 11:4 “By faith Abel offered to God a better sacrifice than Cain, through which he obtained the testimony that he was righteous, God testifying about his gifts, and though faith, though he is dead, he still speaks.”

Hebrews 11:35 breaks into a whole chapter listing Trophies of Grace: “..and others were tortured, not accepting their release in order that they might obtain a better resurrection; 36. and others experienced mockings and scourgings, yes, also chains and imprisonment. 37. They were stoned, they were sawn in two, they were tempted, they were put to death with the sword; they went about in sheepskins, in goatskins, being destitute, afflicted, ill-treated 38. (men of whom the world was not worthy), wandering in deserts and mountains and caves and holes in the ground. 39. And all these, having gained approval through their faith...”
They were Old Testament Christians. Their faith was in the promises of the coming Redeemer, Jesus Christ, in the same way we are Christians looking back at Christ's finished work at Calvary, His resurrection and ascension into Glory.
“That where I Am, you may be also.”

I suggest that you read the rest of John 1. Specifically:

John 1:
14 The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the one and only Son, who came from the Father, full of grace and truth. 15 (John testified concerning him. He cried out, saying, “This is the one I spoke about when I said, ‘He who comes after me has surpassed me because he was before me.’”)

Now ... did Abel live and die before, or after "The Word became flesh"?

The answer, obviously is "before". God the Son, The Word, had NOT "become flesh" at the time of Abel. To say that "Christ", that is the Anointed One, the Word made Flesh, was around at the time of Abel is to depart from Christianity.