With these introductory concepts in mind, let's consider a brief history of the old-earth and young-earth positions.
 

The Young-Earth View.

For thousands of years, the vast majority of those who believed the Bible to be the Word of God also believed that the Bible taught that God created the universe in six literal days, approximately 4000 years before the birth of Christ.

In particular, Bible scholars who were experts in the Hebrew language concluded that the "days" of Genesis 1 and Exodus 20:11 were clearly intended to be normal (24 hour) solar days. They also held that Genesis 5:3-32 and 11:10-26 were an accurate historical record of the descendants of Adam, which provided the information needed to calculate the number of years that passed from Adam to Abraham (i.e. the age of the father at the birth of the son in the genealogy).

Moreover, they accepted the Biblical teaching that a global flood occurred in the days of Noah that covered the highest mountains. The various sedimentary rock layers, and the fossils they contained, were naturally believed by Christian scholars to have been laid down by the flood. The idea of a 6-day creation, occurring about 4000 B.C., together with a global flood, was virtually the universal view[1] of Jews and Christians until about 1800, when some new ideas began circulating in the scientific community.
 

The Old-Earth View.

In 1779, the French geologist, Comte de Buffon[2] published a book (Epochs of Nature) which suggested that the earth was once a hot molten ball that cooled to its present state over 75,000 years. In 1796, Pierre Laplace advanced his Nebular Hypothesis in a book titled Exposition of the System of the Universe. In 1809, Jean Lamarck put forth a theory of biological evolution over long ages in his Philosophy of Zoology.

In 1795, James Hutton published his book Theory of the Earth, which proposed that the land masses were the result of cyclical erosion, deposition and uplift. From 1815 to 1817, William Smith published three works which proposed that the age of rock layers could be determined from certain "index fossils" that appeared in them. He is sometimes called the "Father of English Stratigraphy".

In 1830-1833, Charles Lyell published his 3-volume work, Principles of Geology, in which he advanced the idea of uniformitarianism— namely, that present-day rates and intensities of processes should be used to interpret geologic history. This was a radical departure from the formerly accepted idea of catastrophism— i.e. that geological catastrophes of major proportion were responsible for shaping much of geologic history.

It should be noted that all of these theories were speculative in nature, and that none were actually proven to be true. They were more an indicator of the prevailing philosophical climate and attitudes of their time, and of men's desire for an alternative explanation of earth history than the one given in scripture.

The movement gradually gained momentum, and especially found acceptance once Darwin's Origin of Species began to be widely embraced, since these theories seemed to provide sufficient time to allow biological evolution to occur.[3]
 

Accommodation Theories.

While the scientific community was becoming enthralled with these unproven secular theories, the church was starting to feel pressure to conform its teachings to these new ideas. In 1804, Thomas Chalmers set forth the "Gap Theory" (also known as the "Ruin-Reconstruction Theory"), which tried to fit millions of years between Genesis 1:1 and 1:2. In 1823, George Stanley Faber proposed the "Day-Age Theory", suggesting that the "days" of Genesis 1 were not literal days, but long ages.

Christians likewise began to revise the flood story to make it fit the geological theories. In the 1820's, John Fleming proposed the "Tranquil Flood" theory, which said that the flood left no lasting geological evidence. John Pye Smith offered an alternative— the "Local Flood" theory— suggesting that the flood was a local event in the Middle east.

Like the geological theories that had prompted these "accommodation theories", there was no independent geological evidence to support them. These were simply speculative theories invented to resolve what was perceived as an inconsistency between science and the Bible.

Moreover, these accommodation theories required major reworking of various scripture passages. The Bible gives no hint of a "gap" between Genesis 1:1 and 1:2. Promoters of the Gap Theory claimed that the statement "… the earth was without form and void …" should be translated "… the earth became without form and void …", because in a few passages, the word "was" could perhaps mean "came to be". They also cited Isaiah 45:18 to show that the original creation was not "formless and void", so that Genesis 1:2 must be describing a judgment of God upon the world before the six days began.[4] They imagined (with no explicit Biblical support) that the world had been inhabited by a pre-Adamic race of hominids who were led by Satan to rebel against God and thus fell under God's judgment. They cited Genesis 1:28 in which, in the King James Version, God commanded Adam and Eve to "replenish" the earth— arguing that the earth must once have been filled, if they were now to re-fill the earth.[5]

Advocates of the Day Age Theory argued that the Hebrew word "yom" (translated "day" in Genesis 1) is often used to mean a long or indefinite period of time, and is not necessarily a 24-hour day. They further reasoned that each "day" could therefore be thousands or millions of years long, and that this would bring the Biblical teaching into line with the new scientific theories. They cited 2 Peter 3:8 ("with the Lord one day is as a thousand years, and a thousand years as one day") in support of their thesis.

There are several problems with their argument, however. For one, the order of events in the six days of Genesis 1 does not match the order that the scientists were claiming. Genesis says that the earth was formed on day 1 and that the sun, moon and stars were created on day 4. Scientists claimed that the sun and stars were formed first, and that the earth formed later.

Moreover, Genesis 1:5 defines "day" to be a period of light, and "night" to be a period of darkness. If the days of Genesis 1 were millions of years in length, they would be millions of years of light followed by millions of years of darkness, and no living thing would be able to survive such conditions.

Another problem with their theory is that, every other place in scripture where the word "day" is used with "morning" or "evening", it denotes a literal 24-hour solar day. Likewise, when the word "day" is used with ordinal numbers— first, second, third, etc.— it always denotes literal days. And Exodus 20:8-11 bases the 7-day weekly Sabbath on the creation week. Had the "day-age" interpretation been a valid way to handle the text, Hebrew scholars would have recognized this and acknowledged it centuries earlier.

Finally, Peter was not discussing the days of Genesis 1 when he said "with the Lord one day is as a thousand years, and a thousand years as one day". Instead, he was discussing God's patience toward sinners. If it were valid to apply Peter's statement to the six days of creation, then it would be equally valid to apply it to any statement in scripture that mentions days. Perhaps the Israelites actually marched around Jericho for 7000 years, instead of merely 7 days (Joshua 6:1-16). Perhaps God, in Exodus 20:8-11, was commanding the Israelites to observe a 1000-year long Sabbath after working constantly for 6000 years. Perhaps Jesus rose on the 3000th year instead of the third day (Matthew 16:21; 17:23; etc.). Perhaps Pentecost occurred 50,000 years (Acts 1:3-5; 2:1; Leviticus 23:16) after the resurrection. It is arbitrary and unjustified to apply Peter's statement to the days of creation week when that is clearly not the subject under discussion in 2 Peter 3:8, and when this would clearly be an invalid way to understand the "days" of other passages of scripture.

The Tranquil Flood theory likewise cannot endure Biblical or scientific scrutiny. The Bible describes the flood as an extremely violent event— destroying all the land creatures that were not safely inside the ark— and it is difficult to imagine how the entire earth could be flooded— covering the highest mountains— in the space of just 40 days, then remain covered with water for a full year, and yet leave no trace in the rock layers.

The Local Flood theory stands in contradiction to the Bible's affirmation that "… all the high mountains under the whole heaven were covered" (Genesis 7:19) and that the flood waters rose 15 cubits above the highest mountains (Genesis 7:20). Also, there would have been no reason for Noah to spend 100 years building the ark, nor for all the animals to come into the ark, if they could instead have walked to safety in less than a year. The Bible makes it clear that the flood was a worldwide judgment that destroyed all life from the surface of the earth. It is difficult to imagine how He could have stated it any more clearly than this:

And all flesh died that moved on the earth, birds, livestock, beasts, all swarming creatures that swarm on the earth, and all mankind. Everything on the dry land in whose nostrils was the breath of life died. He blotted out every living thing that was on the face of the ground, man and animals and creeping things and birds of the heavens. They were blotted out from the earth. Only Noah was left, and those who were with him in the ark. And the waters prevailed on the earth 150 days.
Genesis 7:21-24

None of these theories fits the text, however. Genesis 1 says that God created, not revealed, on each of the days. The literary style is that of historical narrative, and not poetry— the chapter uses the normal Hebrew construction for sequential events (the waw consecutive). Moreover, the passage clearly intends continuity between the days by connecting each pair of successive days with "evening and morning"— a single night.
 

[1] The only alternative view during this time was one held by Clement of Alexandria, Origen and Augustine, who believed that God created everything in an instant in time, and did not need 6 days, much less millions of years.

[2] For the historical material presented in this and the following paragraphs, see Terry Mortensen, "Chapter 11: Where Did the Idea of 'Millions of Years' Come From?", The New Answers Book 2, (Green Forest, AR: Master Books, 2010), April 22, 2010, http://www.answersingenesis.org/articles/nab2/idea-of-millions-of-years.

[3] We now know that the molecular complexity of life— proteins, DNA, RNA, etc.— is such that billions of billions of years would not have provided nearly sufficient time to obtain the first living cell by chance molecular interactions.  See Appendix A: The Odds of Life Forming by Chance for a treatment of this subject.

[4] The Hebrew word "tohu" (waste or empty) appears in Isaiah 45:18, "he [God] did not create it empty [tohu]", whereas Genesis 1:2 says "The earth was without form [tohu] and void". Superficially, this seems to support the notion that the earth became waste (tohu). However, in context, Isaiah 45:18 is affirming that God had a purpose for creation "he did not create it empty, he formed it to be inhabited"— it does not claim to be describing conditions just prior to Genesis 1:2. God's work of creation was not complete until the end of creation week, during which time he formed and filled the earth.

[5]  The Hebrew word translated "replenish" simply means "fill"— not "re-fill". The King James rendering is misleading. This is the sort of argument that would never have been used if its promoters had simply consulted the Hebrew and Greek (LXX) texts.

[6]  Appendix B critiques yet another accommodation theory that has become quite popular in our day: The Framework Hypothesis.