If the Bible is correct, that we are all decended from Adam and Eve (and, I suppose Noah and Mrs. Noah), then who was the first atheist?

Satan was the first Atheist. Satan will also be the last one laughing at them.

Cain was the first to say to himself, "God is dead. There is no judge." Until God said to him, "Where is your brother Abel," Cain was not afraid. https://youtu.be/ve6P4QzqCGU

the first atheist probably came before the time of noah, when all of humankind did wickedness before God, and it grieved Him. It's not important dear, but what we do know is that it would have been during times of great wickedness, as the 20th century shows us how wicked atheism can get.

And how come we are not all white with identical genes

satan

anyone that says Satan is ignorant.. to believe in Satan is to believe in God.. cause the two come hand in hand in the bible.. satan stood right before God and disobeyed God.. so he wasnt an atheist.. He didnt follow Gods commandments and is a sinner, but he did believe there was a God.. Atheists dont

IMHO, it was probably not one "first" atheist, but several around the world in various tribes and clans during the hunter/gatherer phase that began to realize that all the rituals made to trees and rocks (and later carved objects) had no relationship to reality. If they knew what was good for them, they played along.

Satan

Do you have 'invisible qualities'? Of course you do. So does God. His invisible qualities - His divine nature and eternal wisdom - have been clearly seen by what has been made. He has made them obvious to everybody.... so no one has an excuse. In other words, lying to yourself about it won't change the outcome; and there are no atheists.... just people who choose to DISMISS the knowledge of God as having value to them.

I know... I was like them until I sought God out at age 42 - launching an investigation into the God I heard who 'hated religion'.... because that was a God I WANTED to know.

And now I do. :)

The fool who said there is no God.