What is the Gap theory?

The so-called "Gap Theory" is a conjecture about a possible interval between the first two verses in Genesis 1. Among other things, it attempts to deal with the creation of the angels, the fall of Lucifer, and related topics. According to this theory:

(1). God created a fully-functional earth in Verse 1 which had a very wide range of animal and plant life, including fish, mammals and dinosaurs, and others that are known today only from their fossils;

(2). Satan's fall occurred sometime in the gap between verse 1 and verse 2 (which is why it's called the Gap theory!)

(3). The earth was laid waste as a result of Satan's rebellion;

(4). God remade earth into a paradise again in 6 days of re-creation.

(5). This then harmonizes the Bible account with the fossil record and science.

This theory is not held by many today because of Biblical and theological problems.