(Gen 2:17 KJV) "But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die."
The provision of life was conditional and dependent upon man’s obedience to God. The promise of eternal life was never made to any other earthly creature except for man. God made the animals as brute beasts. They live their brief span of life and they die. Therefore, Adam was familiar with the concept of death.
The day spoken of in Genesis 2:17 is not a 24-hour day. Genesis 5:5 informs us that Adam was 930 years old when he died. So, how did Adam die in the day he sinned? 2 Peter 3:8 reads, “…one day is with the Lord as a thousand years, and a thousand years as one day.” God had told Adam that if he ate of the tree of knowledge, then dying, he would die. Or, Adam would begin the dying process when he sinned and he would completely die within a thousand year day. Thankfully, we see how God has redeemed Adam and all of his children from destruction through the precious blood of Christ, because mankind is so much better than the brute beast.