Let's suppose your ancestors lived in Utah as many of the people I talk to each day do. What are the earliest records in Utah you can find for your family? The answer is 1847, the date the first pioneers arrived in the Salt Lake Valley. This fact underlies a basic limitation on records throughout the world. As we go back in time, there are fewer and fewer records to research concerning families. If your family came from Europe, what are the earliest records of your family in America? Again, that date is certain, it is 1492. Granted, there may be archaeological evidence of earlier European contact, but there are no family history records associated with that early evidence.
As we go back in time doing research about our families, we need to recognize this temporal limitations due both to record loss and the fact that fewer records were actually created. This limitation applies to each county in the United States. For example, I live in Utah County, Utah. If I consult the FamilySearch.org Research Wiki for Utah County, I find the following chart:
For each category of records there is a time limit. Although there may be alternative records to consult and go back further, I will ultimately hit the earliest date when settlers arrived in what is now Utah County. The earliest records for the County date from the date of its formation in 1852, however, the first settlers arrived in 1849.
The Newberry Atlas of Historical County Boundaries lists the earliest dates for each county in the United States.
You can use the same techniques of looking for the earliest records from any location on earth. Now, people rely on the Bible for the genealogy back to Adam. Even if we assume that the genealogies set forth in the Bible are accurate, there must be some records that connect your family back to the Bible genealogies before relying on such a source. Despite the seemingly availability of these records, those that have been used are highly unreliable. Original research back to Adam, whatever your beliefs on the subject, is just not possible.
In every case where someone claims that their pedigree goes "back to Adam," they are relying on Royal Lines. I recently wrote a post updating the connections to royal lines. See "Documenting Royal Ancestry -- An Important Explanation."
What is more important, copying these royal lines distracts us from the really important and interesting research we can do with our documented families.