Seafaring before the Neolithic - circa 7th millennium BCE - is a controversial issue in the Mediterranean. However, evidence from different parts of the Aegean is gradually changing this, revealing the importance of early coastal and island environments. The site of Ouriakos on the island of Lemnos (Greece) tentatively dates to the end of the Pleistocene and possibly the beginning of the Holocene, circa 12,000 BP.
     A team formed by N. Laskaris, A. Sampson and I. Liritzis from the Laboratory of Archaeometry, University of the Aegean, Department of Mediterranean Studies, Rhodes; and F. Mavridis from the Ephorate of Palaeo-anthropology and Speleology of Southern Greece suggested that obsidian sources on the island of Melos in the Cyclades could have been exploited earlier. Studies of material from Franchthi cave in the Argolid indicated Melos as its origin, but obsidian hydration dating was not applied to the artefacts recovered.
     Obsidian, or 'volcanic glass', has been a preferred material for stone tools wherever it is found or traded. It also absorbs water vapour when exposed to air - for instance, when it is shaped into a tool - and absolute or relative dates can be determined for that event by measuring the depth of water penetration. In 10,000 years, the expected hydration depth is about 10 mm from the tool surface.
     Two routes for the obsidian found at Franchthi have been considered: a direct one of around 120 kilometres with islets in between, and another one through Attica including crossings of 15 to 20 kilometres between islands. The presence of obsidian in mainland and island sites indicates that these voyages included successful return journeys.
     Sites in Ikaria, in Sporades, and on Kythnos demonstrate that, during the Mesolithic, a well established system of obsidian exploitation and circulation existed - a phenomenon that has its routes even earlier, as dates from sites in Attica indicate. Furthermore, obsidian artefacts have recently been found in two other Mesolithic sites in Greece, one in the island of Naxos and the other one in the small island of Halki. Exchange systems therefore brought obsidian to the eastern and the north-west Aegean, and even reached coastal inland sites of mainland Greece such as Attica, though not yet found in mainland sites. Possibly through sites in this latter region obsidian was also brought to the Peloponnese.

Edited from Journal of Archaeological Science, Volume 38, Issue 9, pp. 2475-2479 (2011)