Gap theory page - what is the gap theory?

Gap theory page - what is the gap theory?: "What is the gap theory ?
The main idea behind the gap theory is, that lucifer rebelled against God and persuaded 1/3 of all the angels to rebell with him, and in attacking the throne of God, he was thrown out from Gods presence, and stripped of his authority he had with God.
Genesis gives some clues as to the situation in saying that the earth was tohu wa bohu, in Isaiah God says that He did not create the earth like that, but created it to be inhabited, in other words, the earth was not tohu wa bohu in the beginning, but it became like that, which the septuaginta also states."