As I mentioned in my post "This is (not) the End" I hadn't realized that non-biblical source material supported a young earth dating conclusion. If you Google: problems with evolutionary ages you can find all sorts of information on the topic. I'm going to skip the evolutionary problems and address the part of the topic I understand best. What I'm taking a crack at is some of the problems with Young Earth (YE) dating methods and chronologies. You did know that there are scholastic problems with arriving at a YE date of creation that have nothing to do with evolutionary theory, right?
The human race generally accepts certain basic elements of time keeping. In ascending order they are seconds, minutes, hours, days, weeks, months, and years. When talking about large periods of time we generally skip over the minor units minuets, hours etc and we establish larger units like decades, centuries or millennium to group large numbers of years together. Certain time units are near universal, these are; the day, week, month and year. While each week is always made up of seven days, a month is lunar measurement spanning the time it takes for the moon to go through all its phases. The year is the amount of time it takes the earth to make one complete orbit of the sun. None of the three units; the week, month and year, perfectly coordinate with each other. This creates a great deal of confusion when creating calendars and recording events.
The problem of dating gets bigger when you consider that most ancient people didn't have a calendar the way we understand the concept. Traditionally things were dated according to events in a relational comparison. For example, "in the third year of Darius the king, such and such happened" is one very common method of establishing a time line. That method was all well and good, if you had a clue as to when the third year was in relation to where you are in the time line. Very few cultures established something like a Mayan long form calendar. A brief break down of some calendars can be found here.
Two other difficulties come up as well. First most civilizations made no effort to date things that happened before their time. Roman calendars only went back to the founding of Rome. They also were notoriously inaccurate in that they only measured part of the year. Second, successive civilizations didn't always preserve the data of the civilization they replaced. So record keeping often has gaps, sometimes those gaps are large.
The civil calendar we use today is the Gregorian Calendar. This is sometimes called the Christian or Western Calendar. One of the purposes of this calendar was to homogenize historical timeliness as well as provide a more accurate alignment of lunar and solar calendars. Some other considerations were "fixing" the Julian Calendar and eliminating the Jewish influence in Christian beliefs. (That was also a consideration in the Julian Calendar as well). Even though both of these calendars are supposed to harmonize the time keeping of the Christian world, they have several issues that create errors. Which is one of the reasons that Jesus, whose birthdate is supposed to be year zero according to Christian belief, was really born around 4 B.C. according to the Gregorian Calendar.
Biblical dating follows the relational time keeping model common throughout the ancient world. It gives no consideration whatsoever to the "Christian Calendar". Jewish calendars try to present an annualized time line starting in year zero and counting forward to today (year 5773). However in the Bible we actually have several time periods that are non-reflective of civil dating as we understand the concept today. That makes it necessary to try to fit the events in the Bible with the civil calendar. This creates its own problems.
The Bible covers several distinct time periods. Those main periods are: Creation week, pre-fall, pre-flood, post flood, Abraham to captivity, the exodus, the judges, the monarchy, captivity, the restored nation, time of Christ. For the most part one can follow the time line backwards from modern times to the time of Abraham with little difficulty. Archaeology and non-biblical recorded history have several common points that touch multiple events and make it possible to develop a plausible time line to Abraham. After that it gets tricky.
How tricky? The Bible only gives three independent traceable events between Adam and Abraham to use for timeline verification. There is also a problem of linguistics and translation, more on that latter. The three potentially historical events traceable in the Genesis are: 1. The Flood, 2. The division of the landmass into continents and 3. The founding of Babylon and the destruction of the tower of Babal. Of those three events only one (the flood) is widely recorded throughout human experience. While the flood is widely recorded, nobody seems to have put much thought into sticking a date on it. The Flood is widely recognized as a historical event but most civilizations see that record as a prehistorical mythology as opposed to a fixed point in time. Babylon and the tower of babal are historical facts, however the archaeology evidence isn't conclusive as far as fixing a solid date is concerned.
Bishop Ussher calculated the beginning of the earth at 4004 BC, Keppler came up with 3993 BC Melanchthon had 3964 BC and Martin Luther arrived at 3961 BC. That’s a 43 year difference (4004-3961=43). So how did that happen? In part we don't know. Ussher failed to keep his notes and "show his work" so we can't redo his calculations. Part of the problem comes when comparing source documents and translations. Using a Masoretic text (and operating with a certain set of assumptions) you come out closer to 4,000 BC; if you use the Septuagint you arrive at a number closer to 5,000BC. Which is right? We don't know.
All of these difficulties come before we address things like: day age theory (the belief that a day recorded in Genesis chapters 1 and 2 is really a long period of time), generational gap (the fact that not every generation is recorded in some ancient genealogies), the long life spans recorded pre-flood, etc. If we take Ussher's date of 4004 BC and add 2012 to it we get an age of 6,016 years which is 243 years more than the Jews who are using the same book as the Christians to arrive at the same point in time (6,016-5773=243). There are other Christian sources that will give dates that provide an even bigger time spread. I use Ussher because he is the most recognized source.
For some 243 years may seem like a big deal. However, Charles Darwin in his book: On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, originally proposed something in the area of 100,000 years for the age of the universe. I believe today evolutionists are guessing someplace in area of billions and billions of years. Creationists have entire sets of assumptions that they are relying on as do evolutionists. The creationist margin of error, isn't even in the same ball park as the evolutionist when you compare the orders of magnitude in terms of "fudge factor". To me the statement that the earth is less than 10,000 years old is a rational one based on evidence from a reliable source that claims to be a firsthand account. Do I accept this on faith? Yes absolutely. Every other historical statement in the book has been proven true by archeology and historical cross-reference. Why would I suddenly decide that the first book was unreliable?