I was recently directed to some questions about Sin, Satan, and Satan's fall.
Did Satan exist before Adam and Eve? How and when did he fall?
The Scriptures do not specify when God created the angels or when specifically Satan fell.
Jude 6 states: "And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day."
2 Peter 2:4 stats: "For if God spared not the angels that sinned, but cast them down to hell, and delivered them into chains of darkness, to be reserved unto judgment;"
Job 4:18 states: "Behold, he put no trust in his servants; and his angels he charged with folly:"
Thus, we know that some of the angels did fall and that this was due to some foolishness and sin on their part. But the exact timing of their creation is not specified.
Isaiah 14 has sometimes been interpreted as referring to the fall of Satan. There are a few reasons that this view has some weaknesses - particularly in that verse 16 speaks about kingdoms, but it is clear that at the latest Satan fell when only Adam and Eve lived.
Nevertheless, vss. 12-15 may be a reference to the fall of Satan, and may be a comparison between that fall and the fall of the king of Babylon (see vs. 4). In other words, God may be comparing the fall of the king of Babylon to the fall of Satan.
We may speculate that Satan and other angels (who are described as having wings) were created with the winged fowl on the 4th day, or that Satan and the other angels being heavenly bodies (and compared to stars) were created with the stars on the 3rd day, or that the angels were created on the first day when God created the heavens and the earth, or that they were created on the 6th day since Satan is described as a serpent. But all this is speculation, since God does not say.
All we know is that all things were made by God in the space of six days (Exodus 20:11), and therefore the angels were created in this time period.
Did sin exist before Adam and Eve?
It seems sin did not exist before the end of the sixth day, because on the sixth day God saw all that he had made and behold it was very good (Genesis 1:1). How could God say that if there was already sin?
Of course, "sin" is not a thing that has its own existence. Rather it is any lack of conformity to (or violation of) God's law.
It seems clear that Satan's temptation in the Garden of Eden of Eve and by her of Adam was sinful and an act of rebellion on Satan's part.
After all, Satan is clearly identified as the serpent in Revelation 20:2 "And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years," and Revelation 12:9 "And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him."
Moreover, his sins of lying and murdering were there:
Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
After all, because of Satan's lie, Eve was deceived and came under judgment of death, making Satan both liar and simultaneously murderer.
Some people may speculate that it was in this very act that Satan fell - namely that the fall of Satan is timed as immediately before the fall of man. Whether this is the case or not, we simply do not know, because Scripture does not say. One reason to think this is that the Serpent is cursed specifically together with Adam and Eve, but prior to the curse of the earth for Adam's sin (Genesis 3:14).
The only remaining question is how there could be sin before Adam's sin, when Scripture states:
Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
But just as this does not exclude Eve's sin before Adam's sin, so also it does not exclude Satan's sin before Eve's sin. For Adam was made the head of the physical creation. In Adam (not in Eve or in Satan) all mankind fell, and that in context is what Paul is describing.
Scripture tells all we need to know. John assures us that we can read the gospel of John and believe and have eternal life (John 20:31) and the Scriptures teach us that they thoroughly equip us for living the Christian life (2 Timothy 3:17). Nevertheless Scripture does not promise to answer every question we may have about everything. Some things we simply cannot be dogmatic about. We should, therefore, cease to be dogmatic where Scripture ceases revelation.