One of the earliest of the modern attempts by Christians to reconcile the biblical account of the cosmos with science is known as the "gap theory." The gap theory was as a small part of a larger complex view of history and eschatology known as dispensationalism that emerged in the last quarter of the 19th century.
Traditionally, Christians optimistically (or faithfully) believed that the majority of the world's people would embrace the Christian religion. They believed that once the church established the millennial kingdom, Christ would return. This belief became known as postmillennialism, because Christ would return after the millennium. As conservative evangelicals recognized the true scope of unreached peoples around the globe, witnessed the increased secularization of Europe, and experienced the rise of liberalism within mainline denominations, they began to draw the conclusion that the church could not establish the millennial kingdom. In fact, the world seemed to be growing worse. This led to the increasing popularity of premillennialism. According to this view, the world would grow increasingly more decadent and ungodly. Only the return of Christ and the establishment of his kingdom promised to stem the tide of evil.
Most premillennialist theologians extended their pessimistic analysis to the past. They reinterpreted the scriptures in such a way to discern different eras in which God dealt with mankind in different ways. Each era constituted a test of the faithfulness of mankind. And each era ended in judgment for mankind, because he always failed the test. Theologions called these eras dispensations. Their theology became known as dispensational premillennialism.
With the rise of Darwinianism, some of these theologians extended their dispensations back to prehistory. According to this scheme, a gap existed in the biblical narrative betweeen Genesis 1:1 and 1:2. In Genesis 1:1, God created the heavens and the earth. This earth was the prehistoric world of dinosaurs. After an unspecified time, God destroyed this world with a flood alluded to in 2 Peter 3:5-7. Then God began the six day creation of the world as we know it in Genesis 1:2. Throught the use of the "gap theory," early twentieth century Christians accounted for the fossil record and the apparent immense age of the earth while remaining faithful to the six day creation acccount of Genesis.
A chart from Clarence Larkin's modestly titled, Greatest Book on Dispensational Truth in the World
Below are a couple of video trailers that resemble those old science films we suffered through in school in the 1960s. One supports the gap theory while the other opposes it. Interestingly, the "scientist" in the latter video claims that Christian liberals crafted the "gap theory." It shows how far young earth creationism has come when it denounces as liberals fellow fundamentalist Christians who hold different views. It also shows that he knows as little about Christian history as he knows about science.