Archbishop James Ussher researched world history and correlated it to the Bible, publishing his findings in 1650. In other words, in some ways he had better resources than we have today).
Ussher's date is based on calculations the Old Testament record.
While the period from Creation to the flood can be taken directly from Genesis, the period from the flood to the birth of Christ is not so straightforward.
In many history books the years are set down as if the state of the world in 5000 BC was known just as clearly as it was in 1000 BC. Things go very fuzzy around 2000 BC, and the historian must rely on the consensus of opinion to fit things in before that time. Conventional archeological dating applies a consensus for dating things according to time periods - like "early bronze age" etc.
How accurate are these assumptions, and are they (like the geological column) based on some shaky ground?
Now it appears some adjustments might be necessary - like revised editions of virtually every ancient history text.gives a comprehensive record that traces the entire history of the world."When the radiocarbon dating method was first tested, good agreement was found between radiocarbon dates for samples of known age (for example, from Ancient Egyptian contexts).As measurements became more precise, however, it gradually became apparent that there were systematic discrepancies between the dates that were being obtained and those that could be expected from historical evidence.
Pre-historic refers to things for which we have no written records and must be dated by estimation, material, design style or radiometric methods - all of which can be wildly inaccurate.
Historic refers to records - like a recorded line of Kings.