This is article a great read, though I agree more with this section here;
Quote:
"It is even possible that God used tone of voice or something else to convey to Adam the danger of the situation. The same as any parent does to warn a child of a danger the parent doesn’t want it to learn by experience."
Although, older scripture talks of the two angels of death, the "first" death being a mortal death that humans first encounter and the "second" death being separation from God. After reading about this, I always assumed that the "second" death would technically be the older one as it was originally punishment for the angels that rebelled, but it's possible that they were created at the same time and the angel (and concept) of mortal death was created on a sort of standby but not put into motion until Adam and Eve ate the fruit of knowledge of good and evil...
When
did mortal death come into existence? It's a good question.