Reference:
http://www.straightdope.com/classics/a1_166a.html
I believe the answer given was incomplete and imprecise. I must say that I am depending on what Isaac Asimov postulated (or compiled?) in one of his essays.
It certainly seems from
our perspective that the Greeks were interested in large geographic regions; why else would they “separate” Asia and Europe into separate continents? The connection between these two “regions” is hundreds of miles (or hundreds of kilometers) long and, to the north, comes down to a modest mountain chain, the Urals. Ordinarily the connection, if any, between continents is a narrow isthmus. The two isthmuses in the world have been sliced by canals, although not at the precise national/continental designation lines.
Furthermore, the E/A matter involves a potentially unending instability. While the Soviet Union existed it expanded south into Armenian territory at least once. Rather than have two parts of the former extend into Asia, one huge and eastern, the other small and southern, it was decided that “Europe” was redefined a far south as necessary at any time.
The simple truth, according to Asimov, is that while the early Greeks were fully aware of the African/Asian isthmus (and in fact considered Africa to be “Asian”), they knew nothing of the meeting of Asia proper with Europe just beyond the Black Sea, or at least had no idea of the hundreds of miles of connection to the north.
If I may go one step farther trusting the Asimovian thesis, the concept of Africa - meaning the known northern fringe - as a separate continent goes back only as far as the Romans looking across the Mediterranean at Carthage, it’s hated rival. This created a psychological barrier that encouraged people to think of Africa as separate. Just as the Greeks (on what may as well have been called “Europe Minor”) looked across the Aegian Sea at the Persian controlled Anatolian peninsula - Asia Minor as it was known at least by the time of the Roman Empire (the “province of asia”). According to Asimov, Greeks vs. Persian Empire was the first East vs. West cultural and military clash.