Fission track analysis has been used to determine the age and Uranium content of obsidian from sources in South-East Europe and Anatolia, and from archaeological deposits in mesolithic levels at the Franchthi Cave in Southern Greece. It is confirmed that the Franchthi obsidian came from the Aegean island of Melos. This is the earliest positive indication available for maritime travel, and carries the history of seafaring back a thousand years. -- AATA