Definition - Gap Theory:
The gap theory postulates that an indefinite span of time exists between Genesis 1:1 and Genesis 1:2. This time span is usually considered to be quite large (millions of years) and is also reputed to encompass the so-called “geologic ages.” Proponents of the gap theory also postulate that a cataclysmic judgment was pronounced upon the earth during this period as the result of the fall of Lucifer (Satan) and that the ensuing verses of Genesis chapter 1 describe a re-creation or reforming of the earth from a chaotic state and not an initial creative effort on the part of God.
Does Lucifer's Fall Support the Gap Theory?
13 You were in Eden,
the garden of God;
every precious stone adorned you:
ruby, topaz and emerald,
chrysolite, onyx and jasper,
sapphire,  turquoise and beryl. 
Your settings and mountings  were made of gold;
on the day you were created they were prepared.
14 You were anointed as a guardian cherub,
for so I ordained you.
You were on the holy mount of God;
you walked among the fiery stones.
15 You were blameless in your ways
from the day you were created
till wickedness was found in you.
16 Through your widespread trade
you were filled with violence,
and you sinned.
So I drove you in disgrace from the mount of God,
and I expelled you, O guardian cherub,
from among the fiery stones. - Ez 28:13-16
We can see (v 14) that Lucifer (who's name translated means 'morning star') was set in charge over the Garden of Eden. Please note that this was NOT the same mission as Adam's was. Adam was commanded to fill and subdue the earth. But I think Lucifer was to 'watch over the affairs' of the Garden. The bible tells us that Lucifer was the Prince of the power of the air. (Eph 2:2). We know that the air (heaven, atmosphere) was created during the 6 days of creation. I surmise then perhaps that Lucifer was created during the 6 days of creation. If Satan had fallen before the 6 days of creation, then God could not have said....
Gen 1:31 And God saw every thing that he had made, and, behold, it was very good. And the evening and the morning were the sixth day.
So there we have it.... day 6 and ALL IS GOOD.
The bible tells us that Lucifer even celebrated after creation.
Where wast thou when I laid the foundations of the earth? declare, if thou hast understanding. Who hath laid the measures thereof, if thou knowest? or who hath stretched the line upon it? Whereupon are the foundations thereof fastened? or who laid the corner stone thereof; When the morning stars sang together, and all the sons of God shouted for joy?" - Job 38:4-7 (emphasis added)
Note that Lucifer was an angel, therefore he was included in the statement 'all the sons of God'.
Now picture this. Lucifer had a good thing going. He was given the title of Prince of Power of the Air which could have been anytime after the second day of creation) He was God's right hand man (if I can use that term). Then one day God created man. No big deal right? But hold on a second. God created man above the angels. He created man in his OWN image.
1Co 6:2 Do ye not know that the saints shall judge the world? and if the world shall be judged by you, are ye unworthy to judge the smallest matters?
1Co 6:3 Know ye not that we shall judge angels? how much more things that pertain to this life?
Gen 1:27 So God created man in his own image, in the image of God created he him; male and female created he them.
We were created as image bearers. We were created to rule over the angels.
Question: So how does the bible tell us that Lucifer introduced sin into creation?
Isa 14:12 How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations!
Isa 14:13 For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north:
Answer: By setting himself up to be God.
How was this accomplished, or attempted?
Caveat: Now please understand that the following I offer as opinion and there isn't a whole lot of theological support for it, however, there is none against it either. So in part I guess I present this as a possible theory, but I remind the reader that the bible is not exactly forthcoming on this issue.
I believe that, driven by jealousy, Lucifer set out to prove God wrong in his adoration of the 'image bearers'. I believe pure jealousy got the better of Lucifer. Lucifer saw how much God loved man.... so much so that he even created man in HIS own image. The bible does not say that angel's were made in God's image, and by the acknowledgement of God that we will one day govern over the angels and judge the angels, It is clear that angels are quite different in that regard. And so - I believe it was then that Lucifer began his fall from glory. Bent now on corrupting man in order to prove his worth, or better yet, prove that God's faith and love for mankind was unwarranted. He used deception then, and he does it now. His powers are limited to lies and accusation toward us before God. He insults God by causing his beloved creation to rebel against God. He hates us because as 'image bearer's' of God, we remind Lucifer of God. Lucifer was in the Garden (Gen 3:1) because he was set in charge as watchman of the garden (Ez 28:14 - guardian cherub
Lucifer's temptation of man was a success. You can imagine in his heart saying... "Ah HAH..... how good is your wonderful creation called man now God?". I'm sure Lucifer thought that the fall of man would be the end of it, but it wasn't.
God out of love for man gave us a second chance, and banished Lucifer from glory and condemned him to complete and utter damnation.
I believe this in turn flew Lucifer in a rage... a rage of which he has never recovered, nor will.
1Pe 5:8 Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:
Rev 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....
Rev 12:12 Therefore rejoice, ye heavens, and ye that dwell in them. Woe to the inhabitants of the earth and of the sea! for the devil is come down unto you, having great wrath, because he knoweth that he hath but a short time.
If Lucifer fell earlier (in a prior humanity; "gap theory"), why did God not put him away forever as He does at the end of time as told to us in the Book of Revelation? I prostulate that scripture infers that Satan fell after creation. It is by this that we know that God created a 'good' creation for man to live in. His desire was for us to live in 'good' relationship with Him, and in a 'very good' creation that brings Glory and Honour to Him. We sinners can truly know that God planned only good for us and Satan is the problem and not God.
There is no requirement for a 'first' earth, or a gap in theology. In fact we saw that we introduce biblical contradictions if we assume there was a gap. My theory follows the literal sense of the scriptures, and doesn't stretch beyond what seems to be logical in light of and harmonize with the scriptural text. Regardless if you agree with me or not, I hope and pray that you have found it at least thought provoking.
- J.R. Hall