Traditionally, many liberal theologians (e.g. Walter Bruggeman) have separated Genesis into two parts - Genesis 1 - 11 and Genesis 12 - 50. The dividing point begins with Abraham, and the tone of Genesis does change significantly at that point.
In the first 11 chapters, Adam through Noah and Babel represent nearly 2000 years of human history. A broad sweep of characters, tied by chronology of "kings" that closely corresponds with Samaritan and Babylonian myth, places Genesis in a worldwide perspective. Beginning with Abraham, however, the narrative slows down dramatically and focuses on just one guy - Abraham, and three generations of his descendants.
It is thus, for this reason that liberal scholars, having divided the book in two, tend to mythologize the first - the table of nations included - but lend more credence to the geneologies beginning with Abraham. The link summarizes Unger's conclusion that Abraham fits well with what we "know" of the Middle Bronze Age
Interestingly, Matthew's genealogy of Jesus also begins not with Adam, but with Abraham. While Matthew may have simply been trying to show Jesus' Jewish identity, it is also possible that he believed Abraham was simply far enough.
Due to the widespread popularity of Abraham (Muslims, Christians, and Jews all claim lineage), most scholars do not doubt that there was "an Abraham," although there is nothing extra-biblical to pinpoint him to a specific date.
Moses, likewise, is such a revered figure that very few scholars doubt there was "a Moses" but again, pinning him down to an exact date is still an inexact science. Primarily scholars tend to settle on one of two dates - either 1440BC (more closely matching the traditional genealogy) or 1290BC, which tends to be preferred by secular historians. Between Moses and the Kingdom of Israel, however, genealogies would still be expected to be more problematic, as there was no one 'leading authority' at the time. (In any event, neither Aaron nor Moses was in Jesus' line, so for Christians, the point would be a little bit moot.)
The earliest recorded person attested to by name in extra-bibilical authority, however, is David - roughly 1000BC. Beginning with the Steele of David, mentioning his name, theistic evolutionists become sufficiently convinced to pronounce dates with something approaching "certainty" - although even David's historicity was questioned until the end of the 20th Century.