I don't know how much I can help on all this, but it was already here when I first got here.
Adam knew and passed it on to you. Genesis 2 explains how God once again created every creature he had made previously for Adam to watch and name. Paul confirms that truth.
Genesis 2:19
19 And out of the ground the LORD God formed every beast of the field, and every fowl of the air; and brought them unto Adam to see what he would call them: and whatsoever Adam called every living creature, that was the name thereof.
Romans 1:20
20. For since the creation of the world God's invisible qualities--his eternal power and divine nature--have been clearly seen, being understood from what has been made, so that men are without excuse.
Man has been on the planet from the beginning, which makes most scientists guesstimates a little long in the tooth.